Systems and methods for electrosurgery

ABSTRACT

Methods and apparatus for selectively applying electrical energy to a target location within a patient&#39;s body, particularly including tissue in the spine. In a method of the invention high frequency (RF) electrical energy is applied to one or more active electrodes on an electrosurgical probe in the presence of an electrically conductive fluid to remove, contract or otherwise modify the structure of tissue targeted for treatment. In one aspect, a dura mater and spinal cord are insulated from the electrical energy by an insulator positioned on a non-active side of the probe. In another aspect, a plasma is aggressively formed in the electrically conductive fluid by delivering a conductive fluid to a distal end portion of the probe and aspirating the fluid from a location proximal of the return electrode. In another aspect, a distal end of an electrosurgical probe having at least one electrode on a biased, curved, bent, or steerable shaft is guided or steered to a target site within an intervertebral disc having a disc defect for treatment of tissue to be treated at the target site by the selective application of electrical energy thereto.

RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.09/708,962 filed Nov. 8, 2000, now U.S. Pat. No. 6,726,684, which claimsthe benefit of Provisional Patent Application No. 60/204,206 filed May12, 2000, and is a continuation-in-part of U.S. patent application Ser.No. 09/676,194, entitled “Methods for Repairing Damaged IntervertebralDiscs”, filed Sep. 28, 2000, now U.S. Pat. No. 6,602,248.

The present invention is related to commonly assigned co-pendingProvisional Patent Application Nos. 60/062,996 and 60/062,997,non-provisional U.S. patent application Ser. No. 08/970,239 entitled“Electrosurgical Systems and Methods for Treating the Spine,” filed Nov.14, 1997, and Ser. No. 08/977,845 entitled “Systems and Methods forElectrosurgical Dermatological Treatment,” filed on Nov. 25, 1997, U.S.application Ser. No. 08/753,227, filed on Nov. 22, 1996, and PCTInternational Application, U.S. National Phase Serial No.PCT/US94/05168, filed on May 10, 1994, now U.S. Pat. No. 5,697,281,which was a continuation-in-part of application Ser. No. 08/059,681,filed on May 10, 1993, which was a continuation-in-part of applicationSer. No. 07/958,977, filed on Oct. 9, 1992 which was acontinuation-in-part of application Ser. No. 07/817,575, filed on Jan.7, 1992, the complete disclosures of which are incorporated herein byreference for all purposes. The present invention is also related tocommonly assigned U.S. Pat. No. 5,683,366, filed Nov. 22, 1995, and U.S.Pat. No. 5,697,536, filed on Jun. 2, 1995, the complete disclosures ofwhich are incorporated herein by reference for all purposes.

BACKGROUND OF THE INVENTION

The present invention relates generally to the field of electrosurgery,and more particularly to surgical devices and methods which employ highfrequency electrical energy to treat tissue in regions of the spine. Thepresent invention is particularly suited for the treatment of herniateddiscs and other disorders of intervertebral discs. This invention alsorelates to treatment of an intervertebral disc by guiding anelectrosurgical probe to a target site within an intervertebral disc.

The major causes of persistent, often disabling, back pain aredisruption of the disc annulus, chronic inflammation of the disc (e.g.,herniation), or relative instability of the vertebral bodies surroundinga given disc, such as the instability that often occurs due to adegenerative disease. Spinal discs mainly function to cushion and tetherthe vertebrae, providing flexibility and stability to the patient'sspine. Spinal discs comprise a central hydrophilic cushion, the nucleuspulposus, surrounded by a multi-layered ligament, the annulus fibrosus.As discs degenerate, they lose their water content and height, bringingvertebrae closer together. This results in a weakening of the shockabsorption properties of the disc and a narrowing of the nerve openingsin the sides of the spine which may lead to pinching of the nerve root.This disc degeneration can cause back and leg pain. Weakness in theannulus fibrosus of degenerative discs, or disc injury, can allowfragments of the nucleus pulposus to migrate from within the disc intothe annulus fibrosus or the spinal canal. Displaced annulus fibrosus, orprotrusion of the nucleus pulposus, e.g., herniation, may impinge onspinal nerves or nerve roots. The mere proximity of the nucleus pulposusor a damaged annulus to a nerve can cause direct pressure against thenerve, resulting in pain and sensory and motor deficit.

Often, inflammation from disc herniation can be treated successfully bynon-surgical means, such as rest, therapeutic exercise, oralanti-inflammatory medications or epidural injection of corticosteroids.In some cases, the disc tissue is irreparably damaged, therebynecessitating removal of a portion of the disc or the entire disc toeliminate the source of inflammation and pressure. In more severe cases,the adjacent vertebral bodies must be stabilized following excision ofthe disc material to avoid recurrence of the disabling back pain. Oneapproach to stabilizing the vertebrae, termed spinal fusion, is toinsert an interbody graft or implant into the space vacated by thedegenerative disc. In this procedure, a small amount of bone may begrafted and packed into the implants. This allows the bone to growthrough and around the implant, fusing the vertebral bodies andpreventing reoccurrence of the symptoms.

Until recently, spinal discectomy and fusion procedures resulted inmajor operations and traumatic dissection of muscle and bone removal orbone fusion. To overcome the disadvantages of traditional traumaticspine surgery, minimally invasive spine surgery was developed. Inendoscopic spinal procedures, the spinal canal is not violated andtherefore epidural bleeding with ensuring scarring is minimized orcompletely avoided. In addition, the risk of instability from ligamentand bone removal is generally lower in endoscopic procedures than withopen discectomy. Further, more rapid rehabilitation facilitates fasterrecovery and return to work.

Minimally invasive techniques for the treatment of spinal diseases ordisorders include chemonucleolysis, laser techniques and mechanicaltechniques. These procedures generally require the surgeon to form apassage or operating corridor from the external surface of the patientto the spinal disc(s) for passage of surgical instruments, implants andthe like. Typically, the formation of this operating corridor requiresthe removal of soft tissue, muscle or other types of tissue depending onthe procedure (i.e., laparascopic, thoracoscopic, arthroscopic, back,etc.). This tissue is usually removed with mechanical instruments, suchas pituitary rongeurs, curettes, graspers, cutters, drills,microdebriders and the like. Unfortunately, these mechanical instrumentsgreatly lengthen and increase the complexity of the procedure. Inaddition, these instruments might sever blood vessels within thistissue, usually causing profuse bleeding that obstructs the surgeon'sview of the target site.

Once the operating corridor is established, the nerve root is retractedand a portion or all of the disc is removed with mechanical instruments,such as a pituitary rongeur. In addition to the above problems withmechanical instruments, there are serious concerns because theseinstruments are not precise, and it is often difficult, during theprocedure, to differentiate between the target disc tissue, and otherstructures within the spine, such as bone, cartilage, ligaments, nervesand non-target tissue. Thus, the surgeon must be extremely careful tominimize damage to the cartilage and bone within the spine, and to avoiddamaging nerves, such as the spinal nerves and the dura matersurrounding the spinal cord.

Lasers were initially considered ideal for spine surgery because lasersablate or vaporize tissue with heat, which also acts to cauterize andseal the small blood vessels in the tissue. Unfortunately, lasers areboth expensive and somewhat tedious to use in these procedures. Anotherdisadvantage with lasers is the difficulty in judging the depth oftissue ablation. Since the surgeon generally points and shoots the laserwithout contacting the tissue, he or she does not receive any tactilefeedback to judge how deeply the laser is cutting. Because healthytissue, bones, ligaments and spinal nerves often lie within closeproximity of the spinal disc, it is essential to maintain a minimumdepth of tissue damage, which cannot always be ensured with a laser.

Monopolar and bipolar radiofrequency devices have been used in limitedroles in spine surgery, such as to cauterize severed vessels to improvevisualization.

Monopolar devices, however, suffer from the disadvantage that theelectric current will flow through undefined paths in the patient'sbody, thereby increasing the risk of unwanted electrical stimulation toportions of the patient's body. In addition, since the defined paththrough the patient's body has a relatively high impedance (because ofthe large resistance or resistivity of the patient's body), largevoltage differences must typically be applied between the return andactive electrodes in order to generate a current suitable for ablationor cutting of the target tissue. This current, however, mayinadvertently flow along body paths having less impedance than thedefined electrical path, which will substantially increase the currentflowing through these paths, possibly causing damage to or destroyingsurrounding tissue or neighboring peripheral nerves.

There is a need for an apparatus or system including an electrosurgicalinstrument, such as a catheter or probe, wherein the instrument can beintroduced into an intervertebral disc during an endoscopic procedure,and the distal portion of the instrument can be guided to a target sitewithin the disc, wherein the target site can be treated with minimal orno damage to surrounding, non-target tissue. The instant inventionprovides such an electrosurgical system and methods for treating tissueby a cool ablation mechanism involving generation of a plasma in thepresence of an electrically conductive fluid and molecular dissociationof tissue components, as is described in enabling detail hereinbelow.

SUMMARY OF THE INVENTION

The present invention provides systems, apparatus and methods forselectively applying electrical energy to structures within a patient'sbody, such as tissue within or around the spine. The systems and methodsof the present invention are particularly useful for ablation,resection, aspiration, collagen shrinkage and/or hemostasis of tissueand other body structures in open and endoscopic spine surgery.

In one aspect of the invention, a method is provided for treating discswithin a patient's spine. Specifically, a method of the presentinvention comprises positioning at least one active electrode withinclose proximity of a disc in the spine (either endoscopically, orthrough an open procedure). The dura mater tissue that surrounds thespinal cord is insulated from the active electrode(s) and a highfrequency voltage is applied between the active electrode(s) and one ormore return electrodes to apply sufficient energy to the disc tissue toreduce the volume of the disc.

In one embodiment, the high frequency voltage is sufficient to ablate atleast a portion of the nucleus pulposus, either the extruded portionoutside the annulus or a portion or all of the nucleus pulposus withinthe annulus. In another embodiment, the active electrode is advancedinto the annulus and sufficient high frequency voltage is applied tocontract or shrink the collagen fibers within the nucleus pulposus. Thiscauses the pulposus to shrink and withdraw from its impingement on thespinal nerve. In other embodiments, the present invention may be used toboth ablate the extruded portion of the nucleus pulposus, and then tocontract or shrink the inner disc material to allow repair of theannulus.

In a specific configuration, electrically conducting fluid, such asisotonic saline, is directed to the target site between the target disctissue and the active electrode. In monopolar embodiments, theconductive fluid need only be sufficient to surround the activeelectrode, and to provide a layer of fluid between the electrode and thetissue. In bipolar embodiments, the conductive fluid preferablygenerates a current flow path between the active electrode(s) and one ormore return electrodes.

In procedures requiring contraction of tissue, high frequency voltage isapplied to the active electrode(s) to elevate the temperature ofcollagen fibers within the tissue at the target site from bodytemperature (about 37° C.) to a tissue temperature in the range of about45° C. to 90° C., usually about 60° C. to 70° C., to substantiallyirreversibly contract these collagen fibers. In a preferred embodiment,an electrically conductive fluid is provided between the activeelectrode(s) and one or more return electrodes positioned on anelectrosurgical probe proximal to the active electrode(s) to provide acurrent flow path from the active electrode(s) away from the tissue tothe return electrode(s). The current flow path may be generated bydirecting an electrically conductive fluid along a fluid path past thereturn electrode and to the target site, or by locating a viscouselectrically conducting fluid, such as a gel, at the target site, andsubmersing the active electrode(s) and the return electrode(s) withinthe conductive gel. The collagen fibers may be heated either by passingthe electric current through the tissue to a selected depth before thecurrent returns to the return electrode(s) and/or by heating theelectrically conductive fluid and generating a jet or plume of heatedfluid which is directed towards the target tissue. In the latterembodiment, the electric current may not pass into the tissue at all. Inboth embodiments, the heated fluid and/or the electric current elevatesthe temperature of the collagen sufficiently to cause hydrothermalshrinkage of the collagen fibers.

In procedures requiring ablation of tissue, the tissue is removed bymolecular dissociation or disintegration processes. In theseembodiments, the high frequency voltage applied to the activeelectrode(s) is sufficient to vaporize an electrically conductive fluid(e.g., gel or saline) between the active electrode(s) and the tissue.Within the vaporized fluid an ionized plasma is formed, and chargedparticles (e.g., electrons) cause the molecular breakdown ordisintegration of several cell layers of the tissue. This moleculardissociation is accompanied by the volumetric removal of the tissue.This process can be precisely controlled to effect the volumetricremoval of tissue as thin as 10 microns to 150 microns with minimalheating of, or damage to, surrounding or underlying tissue structures. Amore complete description of this phenomenon is described in commonlyassigned U.S. Pat. No. 5,683,366, the complete disclosure of which isincorporated herein by reference.

In another aspect of the invention, the present invention is useful forperforming spinal surgery. The method comprises positioning anelectrosurgical instrument in close proximity to an intervertebral disc.An electrically conductive fluid is delivered toward a distal tip of theelectrosurgical instrument. A high frequency electrical energy isapplied to the active electrode such that the conductive fluid completesa current flow path between the active electrode and a return electrode.The conductive fluid is aspirated through an aspiration lumen positionedproximal of the return electrode. Because the aspiration lumen ispositioned away from the fluid delivery lumen and proximal of the returnelectrode, a plasma can be aggressively created and the tissue can beablated or contracted more efficiently.

The tissue may be completely ablated in situ with the mechanismsdescribed above, or the tissue may be partially ablated and partiallyresected and aspirated from this operating corridor. In a preferredconfiguration, the probe will include one or more aspirationelectrode(s) at or near the distal opening of an aspiration lumen. Inthis embodiment, high frequency voltage is applied between theaspiration electrode(s) and one or more return electrodes (which can bethe same or different electrodes from the ones used to ablate tissue) topartially or completely ablate the tissue fragments as they areaspirated into the lumen, thereby preventing clogging of the lumen andexpediting the tissue removal process. In other configurations, theaspiration electrodes can be disposed within the aspiration lumen.

The present invention offers a number of advantages over currentmechanical and laser techniques for spine surgery. The ability toprecisely control the volumetric removal of tissue results in a field oftissue ablation or removal that is very defined, consistent andpredictable. The shallow depth of tissue heating also helps to minimizeor completely eliminate damage to healthy tissue structures, cartilage,bone and/or spinal nerves that are often adjacent the target tissue. Inaddition, small blood vessels within the tissue are simultaneouslycauterized and sealed as the tissue is removed to continuously maintainhemostasis during the procedure. This increases the surgeon's field ofview, and shortens the length of the procedure. Moreover, since thepresent invention allows for the use of electrically conductive fluid(contrary to prior art bipolar and monopolar electrosurgery techniques),isotonic saline may be used during the procedure. Saline is thepreferred medium for irrigation because it has the same concentration asthe body's fluids and, therefore, is not absorbed into the body as muchas certain other fluids.

Apparatus according to the present invention generally include anelectrosurgical probe or catheter having a shaft with proximal anddistal ends, one or more active electrode(s) at the distal end and oneor more connectors coupling the active electrode(s) to a source of highfrequency electrical energy. For endoscopic spine surgery, the shaftwill typically have a distal end portion sized to fit between adjacentvertebrae in the patient's spine. In some embodiments, the distal endportion can have an active side which has the active electrodes and aninsulated non-active side. In a specific use, the insulator can be usedto protect the dura mater (and spinal column) from iatrogenic injury.

Some embodiments of the electrosurgical probe can include a fluiddelivery element for delivering electrically conductive fluid to theactive electrode(s). The fluid delivery element may be located on theprobe, e.g., a fluid lumen or tube, or it may be part of a separateinstrument. In an exemplary embodiment, the lumen will extend through afluid tube exterior to the probe shaft that ends adjacent the distal tipof the shaft.

Alternatively, an electrically conducting gel or spray, such as a salineelectrolyte or other conductive gel, may be applied to the target site.The electrically conductive fluid will preferably generate a currentflow path between the active electrode(s) and one or more returnelectrodes. In an exemplary embodiment, the return electrode is locatedon the probe and spaced a sufficient distance from the activeelectrode(s) to substantially avoid or minimize current shortingtherebetween and to shield the return electrode from tissue at thetarget site.

In a specific configuration, the electrosurgical probe will include anelectrically insulating electrode support member having a tissuetreatment surface at the distal end of the probe. One or more activeelectrode(s) are coupled to, or integral with, the electrode supportmember such that the active electrode(s) are spaced from the returnelectrode. In one embodiment, the probe includes an electrode arrayhaving a plurality of electrically isolated active electrodes embeddedin the electrode support member such that the active electrodes extendabout 0.2 mm to about 10 mm from the tissue treatment surface of theelectrode support member.

In other embodiments, the probe can include one or more lumens foraspirating the electrically conductive fluid from the target area. In anexemplary embodiment, the lumen will extend along the exterior of theprobe shaft and end proximal of the return electrode. In a specificconfiguration, the aspiration lumen and fluid delivery lumen both extendalong the exterior of the probe shaft in an annular configuration. Thefluid delivery lumen will extend to the distal tip of the shaft whilethe aspiration lumen will extend only to a point proximal of the returnelectrode.

In yet another aspect, the present invention provides a method oftreating an intervertebral disc having a nucleus pulposus and an annulusfibrosus. The method comprises advancing a distal end of anelectrosurgical instrument into the annulus fibrosus. The distal end ofthe electrosurgical instrument is moved, typically biased or steered, toa curved configuration that approximates a curvature of an inner surfaceof the annulus fibrosus. A high frequency voltage is delivered betweenan active electrode and a return electrode that are positioned on thedistal end of the electrosurgical instrument to treat the inner surfaceof the annulus fibrosus.

In yet another aspect, the present invention provides a method oftreating an intervertebral disc. The method comprises positioning adistal end of an electrosurgical probe within close proximity of anouter surface of the intervertebral disc. A high frequency voltage isdelivered between an active electrode and a return electrode. The highfrequency voltage is sufficient to create a channel in the disc tissue.The active electrode is then advanced through the channel created in theintervertebral disc. The distal end of the electrosurgical instrument ismoved to a curved configuration that approximates a curvature of aninner surface of the annulus fibrosus. A high frequency voltage isdelivered between the active electrode and the return electrode to treatthe inner surface of the annulus fibrosus.

In a further aspect, the present invention provides an apparatus fortreating an intervertebral disc. The apparatus comprises a steerabledistal end portion that is moveable to a curved configuration thatapproximates the curvature of the inner surface of an annulus fibrosus.At least one active electrode and a return electrode are positioned onthe distal end of the apparatus. A high frequency energy source isconfigured to create a voltage difference between the active electrodeand the return electrode. Preferably, the return electrode is positionedproximal of the active electrode so as to draw the electric current awayfrom the target tissue.

In another aspect, the present invention provides a method of using anelectrosurgical system for treating a disorder of an intervertebral discof a patient, wherein the electrosurgical system includes a power supplycoupled to at least one active electrode disposed on a shaft distal endof an electrosurgical probe. Such disc disorders include fragmentationand migration of the nucleus pulposus into the annulus fibrosus,discogenic or axial pain, one or more fissures in the annulus fibrosus,or contained herniation (a protrusion of the nucleus pulposus which iscontained within the annulus fibrosus) of the disc. The method includesinserting the shaft distal end within the intervertebral disc such thatthe active electrode is in the vicinity of the tissue targeted fortreatment (fissure, contained herniation, etc.), and thereafter applyinga high frequency voltage between the active electrode and a returnelectrode sufficient to ablate target tissue. In preferred embodiments,the voltage generates a plasma in the vicinity of the target site andtissue at the target site is ablated by the molecular dissociation ofdisc tissue components to form low molecular weight ablationby-products, the latter being readily aspirated from the target site ortissue being treated.

In one embodiment, the shaft may be guided by a combination of axialtranslation of the shaft and rotation of the shaft about itslongitudinal axis. In one aspect of the invention, the shaft has apre-defined curvature, both before and after the shaft has been guidedto the vicinity of the contained herniation. The pre-defined curvaturemay include a first and a second curve in the shaft, the second curvebeing proximal to the first curve.

In another aspect of the invention, the shaft may lack a pre-definedcurvature, and may be bent to a suitable conformation prior to aparticular surgical procedure. In yet another aspect of the invention,the shaft may lack a pre-defined curvature, and the shaft distal end maybe steered during a surgical procedure so as to adopt a suitableconformation, thereby allowing the shaft distal end to be guided to atarget site within an intervertebral disc.

By applying a high frequency voltage between the active electrode andthe return electrode, disc tissue at the target site undergoes moleculardissociation. In one embodiment, the active electrode includes anelectrode head having an apical spike and a cusp, wherein the electrodehead is adapted for providing a high current density in the vicinity ofthe electrode head when a high frequency voltage is applied between theactive electrode and the return electrode. The method may beconveniently performed percutaneously, and one or more stages in thetreatment or procedure may be performed under fluoroscopy to allowvisualization of the shaft within the disc to be treated.

Further aspects, features, and advantages of the present invention willappear from the following description in which the preferred embodimentshave been set forth in detail in conjunction with the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an electrosurgical system incorporatinga power supply and an electrosurgical probe for tissue ablation,resection, incision, contraction and for vessel hemostasis according tothe present invention;

FIG. 2 is a side view of an electrosurgical probe according to thepresent invention;

FIG. 3 is a cross-sectional view of a distal portion of the probe ofFIG. 2;

FIG. 4 is an end view of the probe of FIG. 2, illustrating an array ofactive electrodes;

FIG. 5 is an exploded view of the electrical connections within theprobe of FIG. 2;

FIGS. 6–9 are end views of alternative embodiments of the probe of FIG.2, incorporating aspiration electrode(s);

FIG. 10 is a longitudinal sectional view of the distal portion of anelectrosurgical probe;

FIGS. 11A–11C illustrate an alternative embodiment incorporating a meshelectrode for ablating aspirated tissue fragments;

FIGS. 12–15 illustrate a method of performing a microendoscopicdiscectomy according to the principles of the present invention;

FIG. 16 is a schematic view of the proximal portion of anotherelectrosurgical system for endoscopic spine surgery incorporating anelectrosurgical instrument according to the present invention;

FIG. 17 is an enlarged view of a distal portion of the electrosurgicalinstrument of FIG. 16;

FIG. 18 illustrates a method of ablating a volume of tissue from thenucleus pulposus of a herniated disc with the electrosurgical system ofFIG. 16;

FIG. 19 illustrates a planar ablation probe for ablating tissue inconfined spaces within a patient's body according to the presentinvention;

FIG. 20 illustrates a distal portion of the planar ablation probe ofFIG. 19;

FIG. 21A is a front sectional view of the planar ablation probe,illustrating an array of semi-cylindrical active electrodes;

FIG. 21B is a front sectional view of an alternative planar ablationprobe, illustrating an array of active electrodes having oppositepolarities;

FIG. 22 is a top, partial sectional, view of the working end of theplanar ablation probe of FIG. 19;

FIG. 23 is a side cross-sectional view of the working end of the planarablation probe, illustrating the electrical connection with one of theactive electrodes of FIG. 22;

FIG. 24 is a side cross-sectional view of the proximal end of the planarablation probe, illustrating the electrical connection with a powersource connector;

FIG. 25 is a schematic view illustrating the ablation of meniscus tissuelocated close to articular cartilage between the tibia and femur of apatient with the ablation probe of FIG. 19;

FIG. 26 is an enlarged view of the distal portion of the planar ablationprobe, illustrating ablation or cutting of meniscus tissue;

FIG. 27 illustrates a method of ablating tissue with a planar ablationprobe incorporating a single active electrode;

FIG. 28 is a schematic view illustrating the ablation of soft tissuefrom adjacent surfaces of the vertebrae with the planar ablation probeof the present invention;

FIG. 29 is a perspective view of an alternative embodiment of the planarablation probe incorporating a ceramic support structure with conductivestrips printed thereon;

FIG. 30 is a top partial cross-sectional view of the planar ablationprobe of FIG. 29;

FIG. 31 is an end view of the probe of FIG. 30;

FIGS. 32A and 32B illustrate an alternative cage aspiration electrodefor use with the electrosurgical probes shown in FIGS. 2–11;

FIGS. 33A–33C illustrate an alternative dome shaped aspiration electrodefor use with the electrosurgical probes of FIGS. 2–11;

FIGS. 34–36 illustrates another system and method of the presentinvention for percutaneously contracting collagen fibers within anintervertebral disc with a small, needle-sized instrument;

FIG. 37A illustrates a system having a curved distal tip and aninsulator for protecting adjacent tissue;

FIG. 37B is an end view of one embodiment of the system of FIG. 37A;

FIG. 38 illustrates the probe of FIG. 37A being percutaneouslyintroduced into a target intervertebral disc;

FIG. 39 shows the shaft distal end of the system of FIG. 37A with theshaft distal end located within an intervertebral disc;

FIG. 40 is an electrosurgical probe having a fluid delivery lumen and anaspiration lumen;

FIG. 41 is an end view of the electrosurgical probe of FIG. 40;

FIG. 42 illustrates a system having an aspiration lumen and a fluiddelivery lumen;

FIGS. 43A–43D illustrate four embodiments of electrosurgical probesspecifically designed for treating spinal defects;

FIG. 44 illustrates an electrosurgical system having a dispersive returnpad for monopolar and/or bipolar operations;

FIG. 45 illustrates an electrosurgical probe being inserted into anintervertebral disc;

FIGS. 46A and 46B illustrate the distal tip of the electrosurgical probemoving along an inner surface of the annulus fibrosus;

FIG. 47A is a side view of an electrosurgical probe having a curvedshaft;

FIG. 47B is a side view of the distal end portion of the curved shaft ofFIG. 47A, with the shaft distal end portion within an introducer device;

FIG. 47C is a side view of the distal end portion of the curved shaft ofFIG. 47B in the absence of the introducer device;

FIG. 48A is a side view of the distal end portion of an electrosurgicalprobe showing an active electrode having an apical spike and anequatorial cusp;

FIG. 48B is a cross-sectional view of the distal end portion of theelectrosurgical probe of FIG. 48A;

FIG. 49A shows the distal end portion of the shaft of an electrosurgicalprobe extended distally from an introducer needle;

FIG. 49B illustrates the position of the active electrode in relation tothe inner wall of the introducer needle upon retraction of the activeelectrode within the introducer needle;

FIGS. 50A, 50B show a side view and an end view, respectively, of acurved shaft of an electrosurgical probe, in relation to an introducerneedle;

FIG. 51A shows the proximal end portion of the shaft of anelectrosurgical probe, wherein the shaft includes a plurality of depthmarkings;

FIG. 51B shows the proximal end portion of the shaft of anelectrosurgical probe, wherein the shaft includes a mechanical stop;

FIG. 52A schematically represents a normal intervertebral disc inrelation to the spinal cord;

FIG. 52B schematically represents an intervertebral disc exhibiting aprotrusion of the nucleus pulposus and a concomitant distortion of theannulus fibrosus;

FIG. 52C schematically represents an intervertebral disc exhibiting aplurality of fissures within the annulus fibrosus and a concomitantdistortion of the annulus fibrosus;

FIG. 52D schematically represents an intervertebral disc exhibitingfragmentation of the nucleus pulposus and a concomitant distortion ofthe annulus fibrosus;

FIG. 53 schematically represents translation of a curved shaft of anelectrosurgical probe within the nucleus pulposus for treatment of anintervertebral disc;

FIG. 54 shows a shaft of an electrosurgical probe within anintervertebral disc, wherein the shaft distal end is targeted to aspecific site within the disc;

FIG. 55 schematically represents a series of steps involved in a methodof ablating disc tissue according to the present invention;

FIG. 56 schematically represents a series of steps involved in a methodof guiding an electrosurgical probe to a target site within anintervertebral disc for ablation of targeted disc tissue, according toanother embodiment of the invention;

FIG. 57 shows treatment of an intervertebral disc using anelectrosurgical probe and a separately introduced ancillary device,according to another embodiment of the invention;

FIG. 58 is a side view of an electrosurgical probe having a trackingdevice;

FIG. 59A shows a steerable electrosurgical probe wherein the shaft ofthe probe assumes a substantially linear configuration;

FIG. 59B shows the steerable electrosurgical probe of FIG. 59A, whereinthe shaft distal end of the probe adopts a bent configuration;

FIG. 60 shows a steerable electrosurgical probe and an ancillary deviceinserted within the nucleus pulposus of an intervertebral disc;

FIG. 61A shows the shaft distal end of an electrosurgical probepositioned within an introducer extension tube and within an introducerneedle;

FIG. 61B shows the shaft distal end of the probe of FIG. 61A extendingbeyond the distal end of both the introducer extension tube and theintroducer needle, with the shaft distal end adopting a curvedconfiguration;

FIG. 62A shows the distal end of an introducer extension tube advancedto a first position within an intervertebral disc with the shaft distalend accessing a first region of disc tissue; and

FIG. 62B shows the distal end of the introducer extension tube advancedto a second position within an intervertebral disc with the shaft distalend accessing a second region of disc tissue.

DESCRIPTION OF SPECIFIC EMBODIMENTS

The present invention provides systems and methods for selectivelyapplying electrical energy to a target location within or on a patient'sbody, particularly including tissue or other body structures in thespine. These procedures include laminectomy/disketomy procedures fortreating herniated disks, decompressive laminectomy for stenosis in thelumbosacral and cervical spine, medial facetectomy, posteriorlumbosacral and cervical spine fusions, treatment of scoliosisassociated with vertebral disease, foraminotomies to remove the roof ofthe intervertebral foramina to relieve nerve root compression andcervical and lumbar diskectomies, shrinkage of vertebral support tissue,and the like. These procedures may be performed through open procedures,or using minimally invasive techniques, such as thoracoscopy,arthroscopy, laparascopy or the like.

In the present invention, high frequency (RF) electrical energy isapplied to one or more active electrodes in the presence of electricallyconductive fluid to remove and/or modify the structure of tissuestructures. Depending on the specific procedure, the present inventionmay be used to: (1) volumetrically remove tissue, bone, ligament orcartilage (i.e., ablate or effect molecular dissociation of the bodystructure); (2) cut or resect tissue or other body structures; (3)shrink or contract collagen connective tissue; and/or (4) coagulatesevered blood vessels.

In some procedures, e.g., shrinkage of nucleus pulposus in herniateddiscs, it is desired to shrink or contract collagen connective tissue atthe target site. In these procedures, the RF energy heats the tissuedirectly by virtue of the electrical current flow therethrough, and/orindirectly through the exposure of the tissue to fluid heated by RFenergy, to elevate the tissue temperature from normal body temperatures(e.g., 37° C.) to temperatures in the range of 45° C. to 90° C.,preferably in the range from about 60° C. to 70° C. Thermal shrinkage ofcollagen fibers occurs within a small temperature range which, formammalian collagen is in the range from 60° C. to 70° C. (Deak, G., etal., “The Thermal Shrinkage Process of Collagen Fibres as Revealed byPolarization Optical Analysis of Topooptical Staining Reactions,” ActaMorphologica Acad. Sci. of Hungary, Vol. 15(2), pp 195–208, 1967).Collagen fibers typically undergo thermal shrinkage in the range of 60°C. to about 70° C. Previously reported research has attributed thermalshrinkage of collagen to the cleaving of the internal stabilizingcross-linkages within the collagen matrix (Deak, ibid). It has also beenreported that when the collagen temperature is increased above 70° C.,the collagen matrix begins to relax again and the shrinkage effect isreversed resulting in no net shrinkage (Allain, J. C., et al.,“Isometric Tensions Developed During the Hydrothermal Swelling of RatSkin,” Connective Tissue Research, Vol. 7, pp. 127–133, 1980).Consequently, the controlled heating of tissue to a precise depth iscritical to the achievement of therapeutic collagen shrinkage. A moredetailed description of collagen shrinkage can be found in U.S. patentapplication Ser. No. 08/942,580, filed Oct. 2, 1997, entitled “Systemsand Methods for Electrosurgical Tissue Contraction,” previouslyincorporated herein by reference.

The preferred depth of heating to effect the shrinkage of collagen inthe heated region (i.e., the depth to which the tissue is elevated totemperatures between 60° C. to 70° C.) generally depends on (1) thethickness of the tissue, (2) the location of nearby structures (e.g.,nerves) that should not be exposed to damaging temperatures, and/or (3)the volume of contraction desired to relieve pressure on the spinalnerve. The depth of heating is usually in the range from 0 to 3.5 mm. Inthe case of collagen within the nucleus pulposus, the depth of heatingis preferably in the range from about 0 to about 2.0 mm.

In another method of the present invention, the tissue structures arevolumetrically removed or ablated. In this procedure, a high frequencyvoltage difference is applied between one or more active electrode(s)and one or more return electrodes to develop high electric fieldintensities in the vicinity of the target tissue site. The high electricfield intensities lead to electric field induced molecular breakdown oftarget tissue through molecular dissociation (rather than thermalevaporation or carbonization). Applicant believes that the tissuestructure is volumetrically removed through molecular disintegration oflarger organic molecules into smaller molecules and/or atoms, such ashydrogen, oxides of carbon, hydrocarbons and nitrogen compounds. Thismolecular disintegration completely removes the tissue structure, asopposed to dehydrating the tissue material by the removal of liquidwithin the cells of the tissue and extracellular fluids, as is typicallythe case with electrosurgical desiccation and vaporization.

The high electric field intensities may be generated by applying a highfrequency voltage that is sufficient to vaporize an electricallyconductive fluid over at least a portion of the active electrode(s) inthe region between the distal tip of the active electrode(s) and thetarget tissue. The electrically conductive fluid may be a gas or liquid,such as isotonic saline, delivered to the target site, or a viscousfluid, such as a gel, that is located at the target site. In the latterembodiment, the active electrode(s) are submersed in the electricallyconductive gel during the surgical procedure. Since the vapor layer orvaporized region has a relatively high electrical impedance, itminimizes the current flow into the electrically conducting fluid. Thisionization, under optimal conditions, induces the discharge of energeticelectrons and photons from the vapor layer and to the surface of thetarget tissue. A more detailed description of this cold ablationphenomenon, termed Coblation®, can be found in commonly assigned U.S.Pat. No. 5,683,366 the complete disclosure of which is incorporatedherein by reference.

The present invention applies high frequency (RF) electrical energy inan electrically conductive fluid environment to remove (i.e., resect,cut or ablate) or contract a tissue structure, and to seal transectedvessels within the region of the target tissue. The present invention isparticularly useful for sealing larger arterial vessels, e.g., having adiameter on the order of 1 mm or greater. In some embodiments, a highfrequency power supply is provided having an ablation mode, wherein afirst voltage is applied to an active electrode sufficient to effectmolecular dissociation or disintegration of the tissue, and acoagulation mode, wherein a second, lower voltage is applied to anactive electrode (either the same or a different electrode) sufficientto achieve hemostasis of severed vessels within the tissue. In otherembodiments, an electrosurgical probe is provided having one or morecoagulation electrode(s) configured for sealing a severed vessel, suchas an arterial vessel, and one or more active electrodes configured foreither contracting the collagen fibers within the tissue or removing(ablating) the tissue, e.g., by applying sufficient energy to the tissueto effect molecular dissociation. In the latter embodiments, thecoagulation electrode(s) may be configured such that a single voltagecan be applied to coagulate with the coagulation electrode(s), and toablate or contract with the active electrode(s). In other embodiments,the power supply and electrosurgical probe are configured such that thecoagulation electrode is used when the power supply is in thecoagulation mode (low voltage), and the active electrode(s) are usedwhen the power supply is in the ablation mode (higher voltage).

In the method of the present invention, one or more active electrodesare brought into close proximity to tissue at a target site, and thepower supply is activated in the ablation mode such that sufficientvoltage is applied between the active electrodes and the returnelectrode to volumetrically remove the tissue through moleculardissociation, as described below. During this process, some vesselswithin the tissue may be severed. Smaller vessels will be automaticallysealed with the system and method of the present invention. Largervessels, and those with a higher flow rate, such as arterial vessels,may not be automatically sealed in the ablation mode. In these cases,the severed vessels may be sealed by activating a control (e.g., a footpedal) to reduce the voltage of the power supply into the coagulationmode. In this mode, the active electrodes may be pressed against thesevered vessel to provide sealing and/or coagulation of the vessel.Alternatively, a coagulation electrode located on the same or adifferent probe may be pressed against the severed vessel. Once thevessel is adequately sealed, the surgeon activates a control (e.g.,another foot pedal) to increase the voltage of the power supply backinto the ablation mode.

The present invention is particularly useful for removing or ablatingtissue around nerves, such as spinal or cranial nerves, e.g., the spinalcord and the surrounding dura mater. One of the significant drawbackswith the prior art cutters, graspers, and lasers is that these devicesdo not differentiate between the target tissue and the surroundingnerves or bone. Therefore, the surgeon must be extremely careful duringthese procedures to avoid damage to the bone or nerves within and aroundthe spinal cord. In the present invention, the Coblation® process forremoving tissue results in extremely small depths of collateral tissuedamage as discussed above. This allows the surgeon to remove tissueclose to a nerve without causing collateral damage to the nerve fibers.

In addition to the generally precise nature of the novel mechanisms ofthe present invention, applicant has discovered an additional method ofensuring that adjacent nerves are not damaged during tissue removal.According to the present invention, systems and methods are provided fordistinguishing between the fatty tissue immediately surrounding nervefibers and the normal tissue that is to be removed during the procedure.Peripheral nerves usually comprise a connective tissue sheath, orepineurium, enclosing the bundles of nerve fibers to protect these nervefibers. The outer protective tissue sheath or epineurium typicallycomprises a fatty tissue (e.g., adipose tissue) having substantiallydifferent electrical properties than the normal target tissue, such asthe disc and other surrounding tissue that are, for example, removedfrom the spine during spinal procedures. The system of the presentinvention measures the electrical properties of the tissue at the tip ofthe probe with one or more active electrode(s). These electricalproperties may include electrical conductivity at one, several or arange of frequencies (e.g., in the range from 1 kHz to 100 MHz),dielectric constant, capacitance or combinations of these. In thisembodiment, an audible signal may be produced when the sensingelectrode(s) at the tip of the probe detects the fatty tissuesurrounding a nerve, or direct feedback control can be provided to onlysupply power to the active electrode(s) either individually or to thecomplete array of electrodes, if and when the tissue encountered at thetip or working end of the probe is normal (e.g., non-fatty) tissue basedon the measured electrical properties.

In one embodiment, the current limiting elements (discussed in detailbelow) are configured such that the active electrodes, will shut down orturn off when the electrical impedance reaches a threshold level. Whenthis threshold level is set to the impedance of the fatty tissuesurrounding nerves, the active electrodes will shut off whenever theycome in contact with, or in close proximity to, nerves. Meanwhile, theother active electrodes, which are in contact with or in close proximityto target tissue, will continue to conduct electric current to thereturn electrode. This selective ablation or removal of lower impedancetissue in combination with the Coblation® mechanism of the presentinvention allows the surgeon to precisely remove tissue around nerves orbone.

In addition to the above, applicant has discovered that the Coblation®mechanism of the present invention can be manipulated to ablate orremove certain tissue structures, while having little effect on othertissue structures. As discussed above, the present invention uses atechnique of vaporizing electrically conductive fluid to form a plasmalayer or pocket around the active electrode(s), and then inducing thedischarge of energy from this plasma or vapor layer to break themolecular bonds of the tissue structure. Based on initial experiments,applicants believe that the free electrons within the ionized vaporlayer are accelerated in the high electric fields near the electrodetip(s). When the density of the vapor layer (or within a bubble formedin the electrically conductive liquid) becomes sufficiently low (i.e.,less than approximately 10²⁰ atoms/cm³ for aqueous solutions), theelectron mean free path increases to enable subsequently injectedelectrons to cause impact ionization within these regions of low density(i.e., vapor layers or bubbles). Energy evolved by the energeticelectrons (e.g., 4 eV to 5 eV) can subsequently bombard a molecule andbreak its bonds, dissociating a molecule into free radicals, which thencombine into final gaseous or liquid species.

The energy evolved by the energetic electrons may be varied by adjustinga variety of factors, such as: the number of active electrodes;electrode size and spacing; electrode surface area; asperities and sharpedges on the electrode surfaces; electrode materials; applied voltageand power; current limiting means, such as inductors; electricalconductivity of the fluid in contact with the electrodes; density of thefluid; and other factors. Accordingly, these factors can be manipulatedto control the energy level of the excited electrons. Since differenttissue structures have different molecular bonds, the present inventioncan be configured to break the molecular bonds of certain tissue, whilehaving too low an energy to break the molecular bonds of other tissue.For example, fatty tissue, (e.g., adipose tissue) has double bonds thatrequire a substantially higher energy level than 4 eV to 5 eV to break(typically on the order of about 8 eV). Accordingly, the presentinvention in its current configuration generally does not ablate orremove such fatty tissue. However, the present invention may be used toeffectively ablate cells to release the inner fat content in a liquidform. Of course, factors may be changed such that these double bonds canbe broken (e.g., increasing the voltage or changing the electrodeconfiguration to increase the current density at the electrode tips).

The electrosurgical probe or catheter will comprise a shaft or ahandpiece having a proximal end and a distal end which supports one ormore active electrode(s). The shaft or handpiece may assume a widevariety of configurations, with the primary purpose being tomechanically support the active electrode and permit the treatingphysician to manipulate the electrode from a proximal end of the shaft.The shaft may be rigid or flexible, with flexible shafts optionallybeing combined with a generally rigid external tube for mechanicalsupport. Flexible shafts may be combined with pull wires, shape memoryactuators, and other known mechanisms for effecting selective deflectionof the distal end of the shaft to facilitate positioning of theelectrode(s) or electrode array. The shaft will usually include aplurality of wires or other conductive elements running axiallytherethrough to permit connection of the electrode array to a connectorat the proximal end of the shaft.

For endoscopic procedures within the spine, the shaft will have asuitable diameter and length to allow the surgeon to reach the targetsite (e.g., a disc) by delivering the shaft through the thoracic cavity,the abdomen or the like. Thus, the shaft will usually have a length inthe range of about 5.0 cm to 30.0 cm, and a diameter in the range ofabout 0.2 mm to about 20 mm. Alternatively, the shaft may be delivereddirectly through the patient's back in a posterior approach, which wouldconsiderably reduce the required length of the shaft. In any of theseembodiments, the shaft may also be introduced through rigid or flexibleendoscopes. Specific shaft designs will be described in detail inconnection with the drawings hereinafter.

In one embodiment, the probe may comprise a long, thin needle (e.g., onthe order of about 1 mm in diameter or less) that can be percutaneouslyintroduced through the patient's back directly into the spine (see FIGS.34–36). The needle will include one or more active electrode(s) forapplying electrical energy to tissues within the spine. The needle mayinclude one or more return electrodes, or the return electrode may bepositioned on the patient's back, as a dispersive pad. In eitherembodiment, sufficient electrical energy is applied through the needleto the active electrode(s) to either shrink the collagen fibers withinthe intervertebral disk, or to ablate tissue within the disk.

The current flow path between the active electrode(s) and the returnelectrode(s) may be generated by submerging the tissue site in anelectrically conductive fluid (e.g., within a liquid or a viscous fluid,such as an electrically conductive gel) or by directing an electricallyconductive fluid along a fluid path to the target site (i.e., a liquid,such as isotonic saline, or a gas, such as argon). This latter method isparticularly effective in a dry environment (i.e., the tissue is notsubmerged in fluid) because the electrically conductive fluid provides asuitable current flow path from the active electrode to the returnelectrode. A more complete description of an exemplary method ofdirecting electrically conductive fluid between the active and returnelectrodes is described in U.S. Pat. No. 5,697,536, previouslyincorporated herein by reference.

The electrically conductive fluid should have a threshold conductivityto provide a suitable conductive path between the return electrode(s)and the active electrode(s). The electrical conductivity of the fluid(in units of millisiemens per centimeter or mS/cm) will usually begreater than 0.2 mS/cm, preferably will be greater than 2 mS/cm, andmore preferably greater than 10 mS/cm. In an exemplary embodiment, theelectrically conductive fluid is isotonic saline, which has aconductivity of about 17 mS/cm. Alternatively, the fluid may be anelectrically conductive gel or spray, such as a saline electrolyte gel,a conductive ECG spray, an electrode conductivity gel, an ultrasoundtransmission or scanning gel, or the like. Suitable gels or sprays arecommercially available from Graham-Field, Inc of Hauppauge, N.Y.

In some procedures it may also be necessary to retrieve or aspirate theelectrically conductive fluid after it has been directed to the targetsite. In addition, it may be desirable to aspirate small pieces oftissue that are not completely disintegrated by the high frequencyenergy, or other fluids at the target site, such as blood, mucus, thegaseous products of ablation, etc. Accordingly, the system of thepresent invention will usually include a suction lumen in the probe, oron another instrument, for aspirating fluids from the target site. Inaddition, the invention may include one or more aspiration electrode(s)coupled to the distal end of the suction lumen for ablating, or at leastreducing the volume of, non-ablated tissue fragments that are aspiratedinto the lumen. The aspiration electrode(s) function mainly to inhibitclogging of the lumen that may otherwise occur as larger tissuefragments are drawn therein. The aspiration electrode(s) may bedifferent from the ablation active electrode(s), or the sameelectrode(s) may serve both functions. A more complete description ofprobes incorporating aspiration electrode(s) can be found in commonlyassigned, co-pending patent application Ser. No. 09/010,382 filed Jan.21, 1998, the complete disclosure of which is incorporated herein byreference.

The present invention may use a single active electrode or an electrodearray distributed over a contact surface of a probe. In the latterembodiment, the electrode array usually includes a plurality ofindependently current-limited and/or power-controlled active electrodesto apply electrical energy selectively to the target tissue whilelimiting the unwanted application of electrical energy to thesurrounding tissue and environment resulting from power dissipation intosurrounding electrically conductive liquids, such as blood, normalsaline, electrically conductive gel and the like. The active electrodesmay be independently current-limited by isolating the electrodes fromeach other and connecting each electrode to a separate power source thatis isolated from the other active electrodes. Alternatively, the activeelectrodes may be connected to each other at either the proximal ordistal ends of the probe to form a single wire that couples to a powersource.

In some embodiments, the active electrode(s) have an active portion orsurface with surface geometries shaped to promote the electric fieldintensity and associated current density along the leading edges of theelectrodes. Suitable surface geometries may be obtained by creatingelectrode shapes that include preferential sharp edges, or by creatingasperities or other surface roughness on the active surface(s) of theelectrodes. Electrode shapes according to the present invention caninclude the use of formed wire (e.g., by drawing round wire through ashaping die) to form electrodes with a variety of cross-sectionalshapes, such as square, rectangular, L or V shaped, or the like.Electrode edges may also be created by removing a portion of theelongate metal electrode to reshape the cross-section. For example,material can be ground along the length of a round or hollow wireelectrode to form D or C shaped wires, respectively, with edges facingin the cutting direction. Alternatively, material can be removed atclosely spaced intervals along the electrode length to form transversegrooves, slots, threads or the like along the electrodes.

Additionally or alternatively, the active electrode surface(s) may bemodified through chemical, electrochemical or abrasive methods to createa multiplicity of surface asperities on the electrode surface. Thesesurface asperities will promote high electric field intensities betweenthe active electrode surface(s) and the target tissue to facilitateablation or cutting of the tissue. For example, surface asperities maybe created by etching the active electrodes with etchants having a pHless than 7.0 or by using a high velocity stream of abrasive particles(e.g., grit blasting) to create asperities on the surface of anelongated electrode.

The active electrode(s) are typically mounted in or on an electricallyinsulating electrode support that extends from the electrosurgicalprobe. In some embodiments, the electrode support comprises a pluralityof wafer layers bonded together, e.g., by a glass adhesive or the like,or a single wafer. The wafer layer(s) have conductive strips printedthereon to form the active electrode(s) and the return electrode(s). Inone embodiment, the proximal end of the wafer layer(s) will have anumber of holes extending from the conductor strips to an exposedsurface of the wafer layers for connection to electrical conductor leadtraces in the electrosurgical probe or handpiece. The wafer layerspreferably comprise a ceramic material, such as alumina, and theelectrode will preferably comprise a metallic material, such as gold,copper, platinum, palladium, tungsten, silver or the like. Suitablemultilayer ceramic electrodes are commercially available from e.g.,VisPro Corporation of Beaverton, Oreg.

In one configuration, each individual active electrode in the electrodearray is electrically insulated from all other active electrodes in thearray within the probe and is connected to a power source which isisolated from each of the other active electrodes in the array or tocircuitry which limits or interrupts current flow to the activeelectrode when low resistivity material (e.g., blood, electricallyconductive saline irrigant or electrically conductive gel) causes alower impedance path between the return electrode and the individualactive electrode. The isolated power sources for each individual activeelectrode may be separate power supply circuits having internalimpedance characteristics which limit power to the associated activeelectrode when a low impedance return path is encountered. By way ofexample, the isolated power source may be a user-selectable constantcurrent source. In this embodiment, lower impedance paths willautomatically result in lower resistive heating levels since the heatingis proportional to the square of the operating current times theimpedance. Alternatively, a single power source may be connected to eachof the active electrodes through independently actuatable switches, orby independent current limiting elements, such as inductors, capacitors,resistors and/or combinations thereof. The current limiting elements maybe provided in the probe, connectors, cable, controller or along theconductive path from the controller to the distal tip of the probe.Alternatively, the resistance and/or capacitance may occur on thesurface of the active electrode(s) due to oxide layers which formselected active electrodes (e.g., titanium or a resistive coating on thesurface of metal, such as platinum).

The tip region of the probe may comprise many independent activeelectrodes designed to deliver electrical energy in the vicinity of thetip. The selective application of electrical energy to the conductivefluid is achieved by connecting each individual active electrode and thereturn electrode to a power source having independently controlled orcurrent limited channels. The return electrode(s) may comprise a singletubular member of conductive material proximal to the electrode array atthe tip which also serves as a conduit for the supply of theelectrically conductive fluid between the active and return electrodes.Alternatively, the probe may comprise an array of return electrodes atthe distal tip of the probe (together with the active electrodes) tomaintain the electric current at the tip. The application of highfrequency voltage between the return electrode(s) and the electrodearray results in the generation of high electric field intensities atthe distal tips of the active electrodes with conduction of highfrequency current from each individual active electrode to the returnelectrode. The current flow from each individual active electrode to thereturn electrode(s) is controlled by either active or passive means, ora combination thereof, to deliver electrical energy to the surroundingconductive fluid while minimizing energy delivery to surrounding(non-target) tissue.

The application of a high frequency voltage between the returnelectrode(s) and the active electrode(s) for appropriate time intervalseffects cutting, removing, ablating, shaping, contracting or otherwisemodifying the target tissue. The tissue volume over which energy isdissipated (i.e., a high current density exists) may be preciselycontrolled, for example, by the use of a multiplicity of small activeelectrodes whose effective diameters or principal dimensions range fromabout 5 mm to 0.01 mm, preferably from about 2 mm to 0.05 mm, and morepreferably from about 1 mm to 0.1 mm. Electrode areas for both circularand non-circular electrodes will have a contact area (per activeelectrode) below 25 mm², preferably being in the range from 0.0001 mm²to 1 mm², and more preferably from 0.005 mm² to 0.5 mm². Thecircumscribed area of the electrode array is in the range from 0.25 mm²to 200 mm², preferably from 0.5 mm² to 100 m², and will usually includeat least two isolated active electrodes, preferably at least five activeelectrodes, often greater than ten active electrodes and even fifty ormore active electrodes, disposed over the distal contact surfaces on theshaft. The use of small diameter active electrodes increases theelectric field intensity and reduces the extent or depth of tissueheating as a consequence of the divergence of current flux lines whichemanate from the exposed surface of each active electrode.

The area of the tissue treatment surface can vary widely, and the tissuetreatment surface can assume a variety of geometries, with particularareas and geometries being selected for specific applications. Activeelectrode surfaces can have areas in the range from 0.25 mm² to 75 mm²,usually being from about 0.5 mm² to 40 mm². The geometries can beplanar, concave, convex, hemispherical, conical, linear “in-line” arrayor virtually any other regular or irregular shape. Most commonly, theactive electrode(s) or active electrode(s) will be formed at the distaltip of the electrosurgical probe shaft, frequently being planar,disk-shaped, or hemispherical surfaces for use in reshaping proceduresor being linear arrays for use in cutting. Alternatively oradditionally, the active electrode(s) may be formed on lateral surfacesof the electrosurgical probe shaft (e.g., in the manner of a spatula),facilitating access to certain body structures in endoscopic procedures.

It should be clearly understood that the invention is not limited toelectrically isolated active electrodes, or even to a plurality ofactive electrodes. For example, the array of active electrodes may beconnected to a single lead that extends through the probe shaft to apower source of high frequency current. Alternatively, the probe mayincorporate a single electrode that extends directly through the probeshaft or is connected to a single lead that extends to the power source.The active electrode may have a ball shape (e.g., for tissuevaporization and desiccation), a twizzle shape (for vaporization andneedle-like cutting), a spring shape (for rapid tissue debulking anddesiccation), a twisted metal shape, an annular or solid tube shape orthe like. Alternatively, the electrode may comprise a plurality offilaments, a rigid or flexible brush electrode (for debulking a tumor,such as a fibroid, bladder tumor or a prostate adenoma), a side-effectbrush electrode on a lateral surface of the shaft, a coiled electrode orthe like. In one embodiment, the probe comprises a single activeelectrode that extends from an insulating member, e.g., ceramic, at thedistal end of the probe. The insulating member is preferably a tubularstructure that separates the active electrode from a tubular or annularreturn electrode positioned proximal to the insulating member and theactive electrode.

In some embodiments, the electrode support and the fluid outlet may berecessed from an outer surface of the probe or handpiece to confine theelectrically conductive fluid to the region immediately surrounding theelectrode support. In addition, the shaft may be shaped so as to form acavity around the electrode support and the fluid outlet. This helps toassure that the electrically conductive fluid will remain in contactwith the active electrode(s) and the return electrode(s) to maintain theconductive path therebetween. In addition, this will help to maintain avapor or plasma layer between the active electrode(s) and the tissue atthe treatment site throughout the procedure, which reduces the thermaldamage that might otherwise occur if the vapor layer were extinguisheddue to a lack of conductive fluid. Provision of the electricallyconductive fluid around the target site also helps to maintain thetissue temperature at desired levels.

The voltage applied between the return electrode(s) and the electrodearray will be at high or radio frequency, typically between about 5 kHzand 20 MHz, usually being between about 30 kHz and 2.5 MHz, preferablybeing between about 50 kHz and 500 kHz, more preferably less than 350kHz, and most preferably between about 100 kHz and 200 kHz. The RMS(root mean square) voltage applied will usually be in the range fromabout 5 volts to 1000 volts, preferably being in the range from about 10volts to 500 volts depending on the active electrode size, the operatingfrequency and the operation mode of the particular procedure or desiredeffect on the tissue (i.e., contraction, coagulation or ablation).Typically, the peak-to-peak voltage will be in the range of 10 volts to2000 volts, preferably in the range of 20 volts to 1200 volts and morepreferably in the range of about 40 volts to 800 volts (again, dependingon the electrode size, the operating frequency and the operation mode).

As discussed above, the voltage is usually delivered in a series ofvoltage pulses or alternating current of time varying voltage amplitudewith a sufficiently high frequency (e.g., on the order of 5 kHz to 20MHz) such that the voltage is effectively applied continuously (ascompared with e.g., lasers claiming small depths of necrosis, which aregenerally pulsed about 10 Hz to 20 Hz). In addition, the duty cycle(i.e., cumulative time in any one-second interval that energy isapplied) is on the order of about 50% for the present invention, ascompared with pulsed lasers which typically have a duty cycle of about0.0001%.

The preferred power source of the present invention delivers a highfrequency current selectable to generate average power levels rangingfrom several milliwatts to tens of watts per electrode, depending on thevolume of target tissue being heated, and/or the maximum allowedtemperature selected for the probe tip. The power source allows the userto select the voltage level according to the specific requirements of aparticular spine procedure, arthroscopic surgery, dermatologicalprocedure, ophthalmic procedures, FESS procedure, open surgery or otherendoscopic surgery procedure. A description of a suitable power sourcecan be found in U.S. Provisional Patent Application No. 60/062,997entitled “Systems and Methods for Electrosurgical Tissue and FluidCoagulation,” filed Oct. 23, 1997, the complete disclosure of which isincorporated herein by reference.

The power source may be current limited or otherwise controlled so thatundesired heating of the target tissue or surrounding (non-target)tissue does not occur. In a presently preferred embodiment of thepresent invention, current limiting inductors are placed in series witheach independent active electrode, where the inductance of the inductoris in the range of 10 uH to 50,000 uH, depending on the electricalproperties of the target tissue, the desired tissue heating rate and theoperating frequency. Alternatively, capacitor-inductor (LC) circuitstructures may be employed, as described previously in copending PCTapplication No. PCT/US94/05168, the complete disclosure of which isincorporated herein by reference. Additionally, current limitingresistors may be selected. Preferably, these resistors will have a largepositive temperature coefficient of resistance so that, as the currentlevel begins to rise for any individual active electrode in contact witha low resistance medium (e.g., saline irrigant or conductive gel), theresistance of the current limiting resistor increases significantly,thereby minimizing the power delivery from the active electrode into thelow resistance medium (e.g., saline irrigant, a conductive gel, ornatural body fluids such as blood).

Referring to FIG. 1, an exemplary electrosurgical system 11 fortreatment of tissue in the spine will now be described in detail.Electrosurgical system 11 generally comprises an electrosurgicalhandpiece or probe 10 connected to a power supply 28 for providing highfrequency voltage to a target site, and a fluid source 21 for supplyingelectrically conductive fluid 50 to probe 10. In addition,electrosurgical system 11 may include an endoscope (not shown) with afiber optic head light for viewing the surgical site, particularly inendoscopic spine procedures. The endoscope may be integral with probe10, or it may be part of a separate instrument. The system 11 may alsoinclude a vacuum source (not shown) for coupling to a suction lumen ortube 211 (see FIG. 2) in the probe 10 for aspirating the target site.

As shown, probe 10 generally includes a proximal handle 19 and anelongate shaft 18 having an array 12 of active electrodes 58 at itsdistal end. A connecting cable 34 has a connector 26 for electricallycoupling the active electrodes 58 to power supply 28. The activeelectrodes 58 are electrically isolated from each other and each of theelectrodes 58 is connected to an active or passive control networkwithin power supply 28 by means of a plurality of individually insulatedconductors (not shown). A fluid supply tube 15 is connected to a fluidtube 14 of probe 10 for supplying electrically conductive fluid 50 tothe target site.

Power supply 28 has an operator controllable voltage level adjustment 30to change the applied voltage level, which is observable at a voltagelevel display 32. Power supply 28 also includes first, second and thirdfoot pedals 37, 38, 39 and a cable 36 which is removably coupled topower supply 28. The foot pedals 37, 38, 39 allow the surgeon toremotely adjust the energy level applied to active electrodes 58. In anexemplary embodiment, first foot pedal 37 is used to place the powersupply into the “ablation” mode and second foot pedal 38 places powersupply 28 into the “coagulation” mode. The third foot pedal 39 allowsthe user to adjust the voltage level within the “ablation” mode. In theablation mode, a sufficient voltage is applied to the active electrodesto establish the requisite conditions for molecular dissociation of thetissue, as described elsewhere herein. As discussed above, the requisitevoltage level for ablation will vary depending on the number, size,shape and spacing of the electrodes, the distance to which theelectrodes extend from the support member, etc. Once the surgeon placesthe power supply in the “ablation” mode, voltage level adjustment 30 orthird foot pedal 39 may be used to adjust the voltage level to adjustthe degree or aggressiveness of the ablation.

Of course, it will be recognized that the voltage and modality of thepower supply may be controlled by other input devices. However,applicant has found that foot pedals are convenient methods ofcontrolling the power supply while manipulating the probe during asurgical procedure.

In the coagulation mode, the power supply 28 applies a low enoughvoltage to the active electrodes (or the coagulation electrode) to avoidvaporization of the electrically conductive fluid and subsequentmolecular dissociation of the tissue. The surgeon may automaticallytoggle the power supply between the ablation and coagulation modes byalternatively stepping on foot pedals 37, 38, respectively. This allowsthe surgeon to quickly move between coagulation and ablation in situ,without having to remove his/her concentration from the surgical fieldor without having to request an assistant to switch the power supply. Byway of example, as the surgeon is sculpting or ablating soft tissue inthe ablation mode, the probe typically will simultaneously seal and/orcoagulate any small severed vessels within the tissue. However, largervessels, or vessels with high fluid pressures (e.g., arterial vessels)may not be sealed in the ablation mode. Accordingly, the surgeon cansimply step on foot pedal 38, automatically lowering the voltage levelbelow the threshold level for ablation, and apply sufficient pressureonto the severed vessel for a sufficient period of time to seal and/orcoagulate the vessel. After this is completed, the surgeon may quicklymove back into the ablation mode by stepping on foot pedal 37. Aspecific design of a suitable power supply for use with the presentinvention can be found in U.S. Provisional Patent Application No.60/062,997, entitled “Systems and Methods for Electrosurgical Tissue andFluid Coagulation,” filed Oct. 23, 1997, which is incorporated herein byreference.

FIGS. 2–5 illustrate an exemplary electrosurgical probe 20 constructedaccording to the principles of the present invention. As shown in FIG.2, probe 20 generally includes an elongated shaft 100 which may beflexible or rigid, a handle 204 coupled to the proximal end of shaft 100and an electrode support member 102 coupled to the distal end of shaft100. Shaft 100 preferably comprises a plastic material that is easilymolded into the shape shown in FIG. 2. In an alternative embodiment (notshown), shaft 100 comprises an electrically conducting material, usuallymetal, which is selected from the group comprising tungsten, stainlesssteel alloys, platinum or its alloys, titanium or its alloys, molybdenumor its alloys, and nickel or its alloys. In this embodiment, shaft 100includes an electrically insulating jacket 108, which is typicallyformed as one or more electrically insulating sheaths or coatings, suchas polytetrafluoroethylene, polyimide, and the like. The provision ofelectrically insulating jacket 108 over the shaft prevents directelectrical contact between these metal elements and any adjacent bodystructure or the surgeon. Such direct electrical contact between a bodystructure (e.g., tendon) and an exposed electrode could result inunwanted heating of the structure at the point of contact causingnecrosis.

Handle 204 typically comprises a plastic material that is easily moldedinto a suitable shape for handling by the surgeon. Handle 204 defines aninner cavity (not shown) that houses the electrical connections 250(FIG. 5), and provides a suitable interface for connection to anelectrical connecting cable 22 (see FIG. 1). Electrode support member102 extends from the distal end of shaft 100 (usually about 1 mm to 20mm), and provides support for a plurality of electrically isolatedactive electrodes 104 (see FIG. 4). As shown in FIG. 2, a fluid tube 233extends through an opening in handle 204, and includes a connector 235for connection to a fluid supply source, for supplying electricallyconductive fluid to the target site. Fluid tube 233 is coupled to adistal fluid tube 239 that extends along the outer surface of shaft 100to an opening 237 at the distal end of the probe 20, as discussed indetail below. Of course, the invention is not limited to thisconfiguration. For example, fluid tube 233 may extend through a singlelumen (not shown) in shaft 100, or it may be coupled to a plurality oflumens (also not shown) that extend through shaft 100 to a plurality ofopenings at its distal end. Probe 20 may also include a valve 17(FIG. 1) or equivalent structure for controlling the flow rate of theelectrically conductive fluid to the target site.

As shown in FIGS. 3 and 4, electrode support member 102 has asubstantially planar tissue treatment surface 212 and comprises asuitable insulating material (e.g., ceramic or glass material, such asalumina, zirconia and the like) which could be formed at the time ofmanufacture in a flat, hemispherical or other shape according to therequirements of a particular procedure. The preferred support membermaterial is alumina, available from Kyocera Industrial CeramicsCorporation, Elkgrove, Ill., because of its high thermal conductivity,good electrically insulative properties, high flexural modulus,resistance to carbon tracking, biocompatibility, and high melting point.The support member 102 is adhesively joined to a tubular support member(not shown) that extends most or all of the distance between supportmember 102 and the proximal end of probe 20. The tubular memberpreferably comprises an electrically insulating material, such as anepoxy or silicone-based material.

In a preferred construction technique, active electrodes 104 extendthrough pre-formed openings in the support member 102 so that theyprotrude above tissue treatment surface 212 by the desired distance. Theelectrodes 104 are then bonded to the tissue treatment surface 212 ofsupport member 102, typically by an inorganic sealing material. Thesealing material is selected to provide effective electrical insulation,and good adhesion to both the alumina member 102 and the platinum ortitanium active electrodes 104. The sealing material additionally shouldhave a compatible thermal expansion coefficient and a melting point wellbelow that of platinum or titanium and alumina or zirconia, typicallybeing a glass or glass ceramic.

In the embodiment shown in FIGS. 2–5, probe 20 includes a returnelectrode 112 for completing the current path between active electrodes104 and a high frequency power supply 28 (see FIG. 1). As shown, returnelectrode 112 preferably comprises an annular conductive band coupled tothe distal end of shaft 100 slightly proximal to tissue treatmentsurface 212 of electrode support member 102, typically about 0.5 mm to10 mm and more preferably about 1 mm to 10 mm proximal to surface 212.Return electrode 112 is coupled to a connector 258 (FIG. 5) that extendsto the proximal end of probe 10, where it is suitably connected to powersupply 28 (FIG. 1).

As shown in FIG. 2, return electrode 112 is not directly connected toactive electrodes 104. To complete a current path so that activeelectrodes 104 are electrically connected to return electrode 112,electrically conductive fluid (e.g., isotonic saline) is caused to flowtherebetween. In the representative embodiment, the electricallyconductive fluid is delivered through an external fluid tube 239 toopening 237, as described above. Alternatively, the fluid may bedelivered by a fluid delivery element (not shown) that is separate fromprobe 20. In some microendoscopic discectomy procedures, for example,the trocar cannula may be flooded with isotonic saline and the probe 20will be introduced into this flooded cavity. Electrically conductivefluid will be continually resupplied with a separate instrument tomaintain the conduction path between return electrode 112 and activeelectrodes 104.

In alternative embodiments, the fluid path may be formed in probe 20 by,for example, an inner lumen or an annular gap between the returnelectrode and a tubular support member within shaft 100 (not shown).This annular gap may be formed near the perimeter of the shaft 100 suchthat the electrically conductive fluid tends to flow radially inwardtowards the target site, or it may be formed towards the center of shaft100 so that the fluid flows radially outward. In both of theseembodiments, a fluid source (e.g., a bag of fluid elevated above thesurgical site or having a pumping device), is coupled to probe 20 via afluid supply tube (not shown) that may or may not have a controllablevalve. A more complete description of an electrosurgical probeincorporating one or more fluid lumen(s) can be found in parentapplication U.S. Pat. No. 5,697,281, filed on Jun. 7, 1995, the completedisclosure of which is incorporated herein by reference.

Referring to FIG. 4, the electrically isolated active electrodes 104 arespaced apart over tissue treatment surface 212 of electrode supportmember 102. The tissue treatment surface and individual activeelectrodes 104 will usually have dimensions within the ranges set forthabove. In the representative embodiment, the tissue treatment surface212 has a circular cross-sectional shape with a diameter in the range ofabout 1 mm to 30 mm, usually about 2 mm to 20 mm. The individual activeelectrodes 104 preferably extend outward from tissue treatment surface212 by a distance of about 0.1 mm to 8 mm, usually about 0.2 mm to 4 mm.Applicant has found that this configuration increases the high electricfield intensities and associated current densities around activeelectrodes 104 to facilitate the ablation of tissue as described indetail above.

In the embodiment of FIGS. 2–5, the probe includes a single, largeropening 209 in the center of tissue treatment surface 212, and aplurality of active electrodes (e.g., about 3–15 electrodes) around theperimeter of surface 212 (see FIG. 3). Alternatively, the probe mayinclude a single, annular, or partially annular, active electrode at theperimeter of the tissue treatment surface. The central opening 209 iscoupled to a suction or aspiration lumen 213 (see FIG. 2) within shaft100 and a suction tube 211 (FIG. 2) for aspirating tissue, fluids and/orgases from the target site. In this embodiment, the electricallyconductive fluid generally flows from opening 237 of fluid tube 239radially inward past active electrodes 104 and then back through thecentral opening 209 of support member 102. Aspirating the electricallyconductive fluid during surgery allows the surgeon to see the targetsite, and it prevents the fluid from flowing into the patient's body,e.g., into the spine, the abdomen or the thoracic cavity. Thisaspiration should be controlled, however, so that the conductive fluidmaintains a conductive path between the active electrode(s) and thereturn electrode.

Of course, it will be recognized that the distal tip of probe may have avariety of different configurations. For example, the probe may includea plurality of openings 209 around the outer perimeter of tissuetreatment surface 212 (this embodiment not shown in the drawings). Inthis embodiment, the active electrodes 104 extend from the center oftissue treatment surface 212 radially inward from openings 209. Theopenings are suitably coupled to fluid tube 233 for deliveringelectrically conductive fluid to the target site, and aspiration lumen213 for aspirating the fluid after it has completed the conductive pathbetween the return electrode 112 and the active electrodes 104.

In some embodiments, the probe 20 will also include one or moreaspiration electrode(s) coupled to the aspiration lumen for inhibitingclogging during aspiration of tissue fragments from the surgical site.As shown in FIG. 6, one or more of the active electrodes 104 maycomprise loop electrodes 140 that extend across distal opening 209 ofthe suction lumen within shaft 100. In the representative embodiment,two of the active electrodes 104 comprise loop electrodes 140 that crossover the distal opening 209. Of course, it will be recognized that avariety of different configurations are possible, such as a single loopelectrode, or multiple loop electrodes having different configurationsthan shown. In addition, the electrodes may have shapes other thanloops, such as the coiled configurations shown in FIGS. 6 and 7.Alternatively, the electrodes may be formed within suction lumenproximal to the distal opening 209, as shown in FIG. 8. The mainfunction of loop electrodes 140 is to ablate portions of tissue that aredrawn into the suction lumen to prevent clogging of the lumen.

Loop electrodes 140 are electrically isolated from the other activeelectrodes 104, which can be referred to hereinafter as the ablationelectrodes 104. Loop electrodes 140 may or may not be electricallyisolated from each other. Loop electrodes 140 will usually extend onlyabout 0.05 mm to 4 mm, preferably about 0.1 mm to 1 mm from the tissuetreatment surface of electrode support member 104.

Referring now to FIGS. 7 and 8, alternative embodiments for aspirationelectrodes will now be described. As shown in FIG. 7, the aspirationelectrodes may comprise a pair of coiled electrodes 150 that extendacross distal opening 209 of the suction lumen. The larger surface areaof the coiled electrodes 150 usually increases the effectiveness of theelectrodes 150 on tissue fragments passing through opening 209. In FIG.8, the aspiration electrode comprises a single coiled electrode 154passing across the distal opening 209 of suction lumen. This singleelectrode 154 may be sufficient to inhibit clogging of the suctionlumen. Alternatively, the aspiration electrodes may be positioned withinthe suction lumen proximal to the distal opening 209. Preferably, theseelectrodes are close to opening 209 so that tissue does not clog theopening 209 before it reaches electrode 154. In this embodiment, aseparate return electrode 156 may be provided within the suction lumento confine the electric currents therein.

Referring to FIG. 10, another embodiment of the present inventionincorporates an aspiration electrode 160 within the aspiration lumen 162of the probe. As shown, the electrode 160 is positioned just proximal ofdistal opening 209 so that the tissue fragments are ablated as theyenter lumen 162. In the representative embodiment, the aspirationelectrode 160 comprises a loop electrode that stretches across theaspiration lumen 162. However, it will be recognized that many otherconfigurations are possible.

In this embodiment, the return electrode 164 is located outside of theprobe as in the previously described embodiments. Alternatively, thereturn electrode(s) may be located within the aspiration lumen 162 withthe aspiration electrode 160. For example, the inner insulating coating163 may be exposed at portions within the lumen 162 to provide aconductive path between this exposed portion of return electrode 164 andthe aspiration electrode 160. The latter embodiment has the advantage ofconfining the electric currents to within the aspiration lumen. Inaddition, in dry fields in which the conductive fluid is delivered tothe target site, it is usually easier to maintain a conductive fluidpath between the active and return electrodes in the latter embodimentbecause the conductive fluid is aspirated through the aspiration lumen162 along with the tissue fragments.

Referring to FIG. 9, another embodiment of the present inventionincorporates a wire mesh electrode 600 extending across the distalportion of aspiration lumen 162. As shown, mesh electrode 600 includes aplurality of openings 602 to allow fluids and tissue fragments to flowthrough into aspiration lumen 162. The size of the openings 602 willvary depending on a variety of factors. The mesh electrode may becoupled to the distal or proximal surfaces of ceramic support member102. Wire mesh electrode 600 comprises a conductive material, such asplatinum, titanium, tantalum, steel, stainless steel, tungsten, copper,gold or the like. In the representative embodiment, wire mesh electrode600 comprises a different material having a different electric potentialthan the active electrode(s) 104. Preferably, mesh electrode 600comprises steel and active electrode(s) 104 comprises tungsten.Applicant has found that a slight variance in the electrochemicalpotential of mesh electrode 600 and active electrode(s) 104 improves theperformance of the device. Of course, it will be recognized that themesh electrode may be electrically insulated from active electrode(s) asin previous embodiments

Referring now to FIGS. 11A–11C, an alternative embodiment incorporatinga metal screen 610 is illustrated. As shown, metal screen 610 has aplurality of peripheral openings 612 for receiving active electrodes104, and a plurality of inner openings 614 for allowing aspiration offluid and tissue through opening 609 of the aspiration lumen. As shown,screen 610 is press fitted over active electrodes 104 and then adheredto shaft 100 of probe 20. Similar to the mesh electrode embodiment,metal screen 610 may comprise a variety of conductive metals, such asplatinum, titanium, tantalum, steel, stainless steel, tungsten, copper,gold, or the like. In the representative embodiment, metal screen 610 iscoupled directly to, or integral with, active electrode(s) 104. In thisembodiment, the active electrode(s) 104 and the metal screen 610 areelectrically coupled to each other.

FIGS. 32A–B and 33A–C illustrate alternative embodiments of the mesh andscreen aspiration electrodes. As shown in FIGS. 32A and 32B, the probemay include a conductive cage electrode 620 that extends into theaspiration lumen 162 (not shown) to increase the effect of the electrodeon aspirated tissue. FIGS. 33A–33C illustrate a dome-shaped screenelectrode 630 that includes one or more anchors 632 (four in therepresentative embodiment) for attaching the screen electrode 630 to aconductive spacer 634. Screen electrode 630 includes a plurality ofholes 631 for allowing fluid and tissue fragments to pass therethroughto aspiration lumen 162. Screen electrode 630 is sized to fit withinopening 609 of aspiration lumen 162 except for the anchors 632 whichinclude holes 633 for receiving active electrodes 104. Spacer 634includes peripheral holes 636 for receiving active electrodes 104 and acentral hole 638 aligned with suction lumen 162. Spacer 634 may furtherinclude insulated holes 640 for electrically isolating screen electrode630 from active electrodes 104. As shown in FIG. 33C, dome-shaped screenelectrode 630 preferably extends distally from the probe shaft 100 aboutthe same distance as the active electrodes 104. Applicant has found thatthis configuration enhances the ablation rate for tissue adjacent toactive electrodes 104, while still maintaining the ability to ablateaspirated tissue fragments passing through screen 630.

FIG. 5 illustrates the electrical connections 250 within handle 204 forcoupling active electrodes 104 and return electrode 112 to the powersupply 28. As shown, a plurality of wires 252 extend through shaft 100to couple electrodes 104 to a plurality of pins 254, which are pluggedinto a connector block 256 for coupling to a connecting cable 22 (FIG.1). Similarly, return electrode 112 is coupled to connector block 256via a wire 258 and a plug 260.

In some embodiments of the present invention, the probe 20 furtherincludes an identification element that is characteristic of theparticular electrode assembly so that the same power supply 28 can beused for different electrosurgical operations. In one embodiment, forexample, the probe 20 includes a voltage reduction element or a voltagereduction circuit for reducing the voltage applied between the activeelectrodes 104 and the return electrode 112. The voltage reductionelement serves to reduce the voltage applied by the power supply so thatthe voltage between the active electrodes and the return electrode islow enough to avoid excessive power dissipation into the electricallyconducting medium and/or ablation of the soft tissue at the target site.The voltage reduction element primarily allows the electrosurgical probe20 to be compatible with various generator or power supply models thatare adapted to apply higher voltages for ablation, moleculardissociation, or vaporization of tissue (e.g., generators supplied byArthroCare Corporation, Sunnyvale, Calif.). For contraction of tissue,for example, the voltage reduction element will serve to reduce avoltage of about 100 to 135 volts rms (which is a setting of 1 on theArthroCare Model 970 and 980 (i.e., 2000) Generators) to about 45 to 60volts rms, which is a suitable voltage for contraction of tissue withoutablation (e.g., without molecular dissociation) of the tissue.

Of course for some procedures in endoscopic spine surgery, the probewill typically not require a voltage reduction element. Alternatively,the probe may include a voltage increasing element or circuit, ifdesired.

In the representative embodiment, the voltage reduction elementcomprises a pair of capacitors forming a bridge divider (not shown)coupled to the power supply and coagulation electrode 380. Thecapacitors usually have a capacitance of about 200 pF to 500 pF (at 500volts) and preferably about 300 pF to 350 pF (at 500 volts). Of course,the capacitors may be located in other places within the system, such asin, or distributed along the length of, the cable, the generator, theconnector, etc. In addition, it will be recognized that other voltagereduction elements, such as diodes, transistors, inductors, resistors,capacitors or combinations thereof, may be used in conjunction with thepresent invention. For example, the probe 350 may include a codedresistor (not shown) that is constructed to lower the voltage appliedbetween the return and coagulation electrodes 360, 380, respectively. Inaddition, electrical circuits may be employed for this purpose.

Alternatively or additionally, the cable 22 that couples the powersupply 28 to probe 20/90 may be used as a voltage reduction element. Thecable has an inherent capacitance that can be used to reduce the powersupply voltage if the cable is placed into the electrical circuitbetween the power supply, the active electrodes and the returnelectrode. In this embodiment, the cable 22 may be used alone, or incombination with one of the voltage reduction elements discussed above,e.g., a capacitor.

In some embodiments, probe 20/90 will further include a switch (notshown) or other input that allows the surgeon to couple and decouple theidentification element to the rest of the electronics in probe 20/90.For example, if the surgeon would like to use the same probe forablation of tissue and contraction of tissue in the same procedure, thiscan be accomplished by manipulating the switch. Thus, for ablation oftissue, the surgeon will decouple the voltage reduction element from theelectronics so that the full voltage applied by the power source isapplied to the electrodes on the probe. When the surgeon desires toreduce the voltage to a suitable level for contraction of tissue, he/shecouples the voltage reduction element to the electronics to reduce thevoltage applied by the power supply to the active electrodes.

Further, it should be noted that the present invention can be used witha power supply that is adapted to apply a voltage within the selectedrange for treatment of tissue. In this embodiment, a voltage reductionelement or circuitry may not be desired.

The present invention is particularly useful in microendoscopicdiscectomy procedures, e.g., for decompressing a nerve root with alumbar discectomy. As shown in FIGS. 12–15, a percutaneous penetration270 is made in the patients' back 272 so that the superior lamina 274can be accessed. Typically, a small needle (not shown) is used initiallyto localize the disc space level, and a guidewire (not shown) isinserted and advanced under lateral fluoroscopy to the inferior edge ofthe lamina 274. Sequential cannulated dilators 276 are inserted over theguide wire and each other to provide a hole from percutaneouspenetration 270 to the lamina 274. The first dilator may be used to“palpate” the lamina 274, assuring proper location of its tip betweenthe spinous process and facet complex just above the inferior edge ofthe lamina 274. As shown in FIG. 13, a tubular retractor 278 is thenpassed over the largest dilator down to the lamina 274. The dilators 276are removed, establishing an operating corridor within the tubularretractor 278.

As shown in FIG. 13, an endoscope 280 is then inserted into the tubularretractor 278 and a ring clamp 282 is used to secure the endoscope 280.Typically, the formation of the operating corridor within retractor 278requires the removal of soft tissue, muscle or other types of tissuethat were forced into this corridor as the dilators 276 and retractor278 were advanced down to the lamina 274. In procedures of the priorart, this tissue has usually been removed with mechanical instruments,such as pituitary rongeurs, curettes, graspers, cutters, drills,microdebriders and the like. Unfortunately, these mechanical instrumentsgreatly lengthen and increase the complexity of the procedure. Inaddition, these instruments sever blood vessels within this tissue,usually causing profuse bleeding that obstructs the surgeon's view ofthe target site.

According to the present invention, an electrosurgical probe or catheter284 as described above is introduced into the operating corridor withinthe retractor 278 to remove the soft tissue, muscle and otherobstructions from this corridor so that the surgeon can easily accessand visualize the lamina 274. Once the surgeon has introduced the probe284, electrically conductive fluid 285 is delivered through tube 233 andopening 237 to the tissue (see FIG. 2). The fluid flows past the returnelectrode 112 to the active electrodes 104 at the distal end of theshaft. The rate of fluid flow is controlled with valve 17 (FIG. 1) suchthat the zone between the tissue and electrode support 102 is constantlyimmersed in the fluid. The power supply 28 is then turned on andadjusted such that a high frequency voltage difference is appliedbetween active electrodes 104 and return electrode 112. The electricallyconductive fluid provides the conduction path (see current flux lines)between active electrodes 104 and the return electrode 112.

The high frequency voltage is sufficient to convert the electricallyconductive fluid (not shown) between the target tissue and activeelectrode(s) 104 into an ionized vapor layer or plasma (not shown). As aresult of the applied voltage difference between active electrode(s) 104and the target tissue (i.e., the voltage gradient across the plasmalayer), charged particles in the plasma (e.g., electrons) causedissociation of the molecular bonds within tissue structures. Thismolecular dissociation is accompanied by the volumetric removal (i.e.,ablative sublimation) of tissue and the production of low molecularweight gases, such as oxygen, nitrogen, carbon dioxide, hydrogen andmethane. This process can be precisely controlled to effect thevolumetric removal of tissue as thin as 10 microns to 150 microns withminimal heating of, or damage to, underlying tissue structures. A moredetailed description of this phenomenon is presented in commonlyassigned U.S. Pat. No. 5,697,882, the complete disclosure of which isincorporated herein by reference.

During the process, the gases will be aspirated through opening 209 andsuction tube 211 to a vacuum source. In addition, excess electricallyconductive fluid, and other fluids (e.g., blood) will be aspirated fromthe operating corridor to facilitate the surgeon's view. During ablationof the tissue, the residual heat generated by the current flux lines(typically less than 150° C.), will usually be sufficient to coagulateany severed blood vessels at the site. If not, the surgeon may switchthe power supply 28 into the coagulation mode by lowering the voltage toa level below the threshold for fluid vaporization, as discussed above.This simultaneous hemostasis results in less bleeding and facilitatesthe surgeon's ability to perform the procedure.

Another advantage of the present invention is the ability to preciselyablate soft tissue without causing necrosis or thermal damage to theunderlying and surrounding tissues, nerves or bone. In addition, thevoltage can be controlled so that the energy directed to the target siteis insufficient to ablate the lamina 274 so that the surgeon canliterally clean the tissue off the lamina 274, without ablating orotherwise effecting significant damage to the lamina.

Referring now to FIGS. 14 and 15, once the operating corridor issufficiently cleared, a laminotomy and medial facetectomy isaccomplished either with conventional techniques (e.g., a Kerrison punchor a high speed drill) or with the electrosurgical probe 284 asdiscussed above. After the nerve root is identified, medical retractioncan be achieved with a retractor 288, or the present invention can beused to ablate with precision the disc. If necessary, epidural veins arecauterized either automatically or with the coagulation mode of thepresent invention. If an annulotomy is necessary, it can be accomplishedwith a microknife or the ablation mechanism of the present inventionwhile protecting the nerve root with the retractor 288. The herniateddisc 290 is then removed with a pituitary rongeur in a standard fashion,or once again through ablation as described above.

In another embodiment, the electrosurgical probe of the presentinvention can be used to ablate and/or contract soft tissue within thedisc 290 to allow the annulus 292 to repair itself to preventreoccurrence of this procedure. For tissue contraction, a sufficientvoltage difference is applied between the active electrodes 104 and thereturn electrode 112 to elevate the tissue temperature from normal bodytemperatures (e.g., 37° C.) to temperatures in the range of 45° C. to90° C., preferably in the range from 60° C. to 70° C. This temperatureelevation causes contraction of the collagen connective fibers withinthe disc tissue so that the nucleus pulposus 291 withdraws into theannulus fibrosus 292.

In one method of tissue contraction according to the present invention,an electrically conductive fluid is delivered to the target site asdescribed above, and heated to a sufficient temperature to inducecontraction or shrinkage of the collagen fibers in the target tissue.The electrically conductive fluid is heated to a temperature sufficientto substantially irreversibly contract the collagen fibers, whichgenerally requires a tissue temperature in the range of about 45° C. to90° C., usually about 60° C. to 70° C. The fluid is heated by applyinghigh frequency electrical energy to the active electrode(s) in contactwith the electrically conducting fluid. The current emanating from theactive electrode(s) 104 heats the fluid and generates a jet or plume ofheated fluid, which is directed towards the target tissue. The heatedfluid elevates the temperature of the collagen sufficiently to causehydrothermal shrinkage of the collagen fibers. The return electrode 112draws the electric current away from the tissue site to limit the depthof penetration of the current into the tissue, thereby inhibitingmolecular dissociation and breakdown of the collagen tissue andminimizing or completely avoiding damage to surrounding and underlyingtissue structures beyond the target tissue site. In an exemplaryembodiment, the active electrode(s) 104 are held away from the tissue asufficient distance such that the RF current does not pass into thetissue at all, but rather passes through the electrically conductivefluid back to the return electrode. In this embodiment, the primarymechanism for imparting energy to the tissue is the heated fluid, ratherthan the electric current.

In an alternative embodiment, the active electrode(s) 104 are broughtinto contact with, or close proximity to, the target tissue so that theelectric current passes directly into the tissue to a selected depth. Inthis embodiment, the return electrode draws the electric current awayfrom the tissue site to limit its depth of penetration into the tissue.Applicant has discovered that the depth of current penetration can alsobe varied with the electrosurgical system of the present invention bychanging the frequency of the voltage applied to the active electrodeand the return electrode. This is because the electrical impedance oftissue is known to decrease with increasing frequency due to theelectrical properties of cell membranes which surround electricallyconductive cellular fluid. At lower frequencies (e.g., less than 350kHz), the higher tissue impedance, the presence of the return electrodeand the active electrode configuration of the present invention(discussed in detail below) cause the current flux lines to penetrateless deeply resulting in a smaller depth of tissue heating. In anexemplary embodiment, an operating frequency of about 100 to 200 kHz isapplied to the active electrode(s) to obtain shallow depths of collagenshrinkage (e.g., usually less than 1.5 mm and preferably less than 0.5mm).

In another aspect of the invention, the size (e.g., diameter orprincipal dimension) of the active electrodes employed for treating thetissue are selected according to the intended depth of tissue treatment.As described previously in copending patent application PCTInternational Application, U.S. National Phase Serial No.PCT/US94/05168, the depth of current penetration into tissue increaseswith increasing dimensions of an individual active electrode (assumingother factors remain constant, such as the frequency of the electriccurrent, the return electrode configuration, etc.). The depth of currentpenetration (which refers to the depth at which the current density issufficient to effect a change in the tissue, such as collagen shrinkage,irreversible necrosis, etc.) is on the order of the active electrodediameter for the bipolar configuration of the present invention andoperating at a frequency of about 100 kHz to about 200 kHz. Accordingly,for applications requiring a smaller depth of current penetration, oneor more active electrodes of smaller dimensions would be selected.Conversely, for applications requiring a greater depth of currentpenetration, one or more active electrodes of larger dimensions would beselected.

FIGS. 16–18 illustrate an alternative electrosurgical system 300specifically configured for endoscopic discectomy procedures, e.g., fortreating extruded or non-extruded herniated discs. As shown in FIG. 16system 300 includes a trocar cannula 302 for introducing a catheterassembly 304 through a percutaneous penetration in the patient to atarget disc in the patient's spine. As discussed above, the catheterassembly 304 may be introduced through the thorax in a thoracoscopicprocedure, through the abdomen in a laparascopic procedure, or directlythrough the patient's back. Catheter assembly 304 includes a catheterbody 306 with a plurality of inner lumens (not shown) and a proximal hub308 for receiving the various instruments that will pass throughcatheter body 306 to the target site. In this embodiment, assembly 304includes an electrosurgical instrument 310 with a flexible shaft 312, anaspiration catheter 314, an endoscope 316 and an illumination fibershaft 318 for viewing the target site. As shown in FIGS. 16 and 17,aspiration catheter 314 includes a distal port 320 and a proximalfitment 322 for attaching catheter 314 to a source of vacuum (notshown). Endoscope 316 will usually comprise a thin metal tube 317 with alens 324 at the distal end, and an eyepiece (not shown) at the proximalend.

In the exemplary embodiment, electrosurgical instrument 310 includes atwist locking stop 330 at a proximal end of the shaft 312 forcontrolling the axial travel distance T_(D) of the probe. As discussedin detail below, this configuration allows the surgeon to “set” thedistance of ablation within the disc. In addition, instrument 310includes a rotational indicator 334 for displaying the rotationalposition of the distal portion of instrument 310 to the surgeon. Thisrotational indicator 334 allows the surgeon to view this rotationalposition without relying on the endoscope 316 if visualization isdifficult, or if an endoscope is not being used in the procedure.

Referring now to FIGS. 17 and 18, a distal portion 340 ofelectrosurgical instrument 310 and catheter body 306 will now bedescribed. As shown, instrument 310 comprises a relatively stiff, butdeflectable electrically insulating support cannula 312 and a workingend portion 348 movably coupled to cannula 312 for rotational andtranslational movement of working end 348. Working end 348 ofelectrosurgical instrument 310 can be rotated and translated to ablateand remove a volume of nucleus pulposus within a disc. Support cannula312 extends through an internal lumen 344 and beyond the distal end 346of catheter body 306. Alternatively, support cannula 312 may be separatefrom instrument 310, or even an integral part of catheter body 306. Thedistal portion of working end 348 includes an exposed return electrode350 separated from an active electrode array 352 by an insulatingsupport member 354, such as ceramic. In the representative embodiment,electrode array 352 is disposed on only one side of ceramic supportmember 354 so that its other side is insulating and thus atraumatic totissue. Instrument 310 will also include a fluid lumen (not shown)having a distal port 360 in working end 348 for delivering electricallyconductive fluid to the target site.

In use, trocar cannula 302 is introduced into a percutaneous penetrationsuitable for endoscopic delivery to the target disc in the spine. Atrephine (not shown) or other conventional instrument may be used toform a channel from the trocar cannula 302 through the annulus fibrosus292 and into the nucleus pulposus. Alternatively, the probe 310 may beused for this purpose, as discussed above. The working end 348 ofinstrument 310 is then advanced through cannula 302 a short distance(e.g., about 7 to 10 mm) into the nucleus pulposus 291, as shown in FIG.18. Once the electrode array 352 is in position, electrically conductivefluid is delivered through distal port 360 to immerse the activeelectrode array 352 in the fluid. The vacuum source may also beactivated to ensure a flow of conductive fluid between electrode array352 past return electrode 350 to suction port 320, if necessary. In someembodiments, the mechanical stop 330 may then be set at the proximal endof the instrument 310 to limit the axial travel distance of working end348. Preferably, this distance will be set to minimize (or completelyeliminate) ablation of the surrounding annulus.

The probe is then energized by applying high frequency voltagedifference between the electrode array 352 and return electrode 350 sothat electric current flows through the conductive fluid from the array352 to the return electrode 350. The electric current causesvaporization of the fluid and ensuing molecular dissociation of thenucleus pulposus tissue as described in detail above. The instrument 310may then be translated in an axial direction forwards and backwards tothe preset limits. While still energized and translating, the workingend 348 may also be rotated to ablate tissue surrounding the electrodearray 352. In the representative embodiment, working end 348 will alsoinclude an inflatable gland 380 opposite electrode array 352 to allowdeflection of working end 348 relative to support cannula 312. As shownin FIG. 18, working end 348 may be deflected to produce a large diameterbore within the nucleus pulposus, which assures close contact withtissue surfaces to be ablated. Alternatively, the entire catheter body306, or the distal end of catheter body 306 may be deflected to increasethe volume of nucleus pulposus removed.

After the desired volume of nucleus pulposus is removed (based on directobservation through port 324, or by kinesthetic feedback from movementof working end 348 of instrument 310), instrument 310 is withdrawn intocatheter body 306 and the catheter body is removed from the patient.Typically, the preferred volume of removed tissue is about 0.2 cm³ to5.0 cm³.

Referring now to FIGS. 19–28, alternative systems and methods forablating tissue in confined (e.g., narrow) body spaces will now bedescribed. FIG. 19 illustrates an exemplary planar ablation probe 400according to the present invention. Similar to the instruments describedabove, probe 400 can be incorporated into electrosurgical system 11 (orother suitable systems) for operation in either the bipolar or monopolarmodalities.

Probe 400 generally includes a support member 402, a distal working end404 attached to the distal end of support member 402 and a proximalhandle 406 attached to the proximal end of support member 402. As shownin FIG. 19, handle 406 includes a handpiece 408 and a power sourceconnector 410 removably coupled to handpiece 408 for electricallyconnecting working end 404 with power supply 28 through cable 34 (seeFIG. 1).

In the embodiment shown in FIG. 19, planar ablation probe 400 isconfigured to operate in the bipolar modality. Accordingly, supportmember 402 or a portion thereof functions as the return electrode andcomprises an electrically conducting material, such as titanium, oralloys containing one or more of nickel, chromium, iron, cobalt, copper,aluminum, platinum, molybdenum, tungsten, tantalum or carbon. In thepreferred embodiment, support member 402 is an austenitic stainlesssteel alloy, such as stainless steel Type 304 from MicroGroup, Inc.,Medway, Mass. As shown in FIG. 19, support member 402 is substantiallycovered by an insulating layer 412 to prevent electric current fromdamaging surrounding tissue. An exposed portion 414 of support member402 functions as the return electrode for probe 400. Exposed portion 414is preferably spaced proximally from active electrodes 416 by a distanceof about 1 mm to 20 mm.

Referring to FIGS. 20 and 21, planar ablation probe 400 furthercomprises a plurality of active electrodes 416 extending from anelectrically insulating spacer 418 at the distal end of support member402. Of course, it will be recognized that probe 400 may include asingle electrode depending on the size of the target tissue to betreated and the accessibility of the treatment site (see FIG. 26, forexample). Insulating spacer 418 is preferably bonded to support member402 with a suitable epoxy adhesive 419 to form a mechanical bond and afluid-tight seal. Electrodes 416 usually extend about 2.0 mm to 20 mmfrom spacer 418, and preferably less than 10 mm. A support tongue 420extends from the distal end of support member 402 to support activeelectrodes 416. Support tongue 420 and active electrodes 416 have asubstantially low profile to facilitate accessing narrow spaces withinthe patient's body, such as the spaces between adjacent vertebrae andbetween articular cartilage and the meniscus in the patient's knee.Accordingly, tongue 420 and electrodes 416 have a substantially planarprofile, usually having a combined height He of less than 4.0 mm,preferably less than 2.0 mm and more preferably less than 1.0 mm (seeFIG. 25). In the case of ablation of meniscus near articular cartilage,the height He of both the tongue 420 and electrodes 416 is preferablybetween about 0.5 mm to 1.5 mm. The width of electrodes 416 and supporttongue 420 will usually be less than 10.0 mm and preferably betweenabout 2.0 mm to 4.0 mm.

Support tongue 420 includes a “non-active” surface 422 opposing activeelectrodes 416 covered with an electrically insulating layer (not shown)to minimize undesirable current flow into adjacent tissue or fluids.Non-active surface 422 is preferably atraumatic, i.e., having a smoothplanar surface with rounded corners, to minimize unwanted injury totissue or nerves in contact therewith, such as disc tissue or the nearbyspinal nerves, as the working end of probe 400 is introduced into anarrow, confined body space. Non-active surface 422 of tongue 420 helpto minimize iatrogenic injuries to tissue and nerves so that working end404 of probe 400 can safely access confined spaces within the patient'sbody.

Referring to FIGS. 21A–B and 22, an electrically insulating supportmember 430 is disposed between support tongue 420 and active electrodes416 to inhibit or prevent electric current from flowing into tongue 420.Insulating member 430 and insulating layer 412 preferably comprise aceramic, glass or glass ceramic material, such as alumina. Insulatingmember 430 is mechanically bonded to support tongue 420 with a suitableepoxy adhesive to electrically insulate active electrodes 416 fromtongue 420. As shown in FIG. 26, insulating member 430 may overhangsupport tongue 420 to increase the electrical path length between theactive electrodes 416 and the insulation covered support tongue 420.

As shown in FIGS. 21A–23, active electrodes 416 are preferablyconstructed from a hollow, round tube, with at least the distal portion432 of electrodes 416 being filed off to form a semi-cylindrical tubewith first and second ends 440, 442 facing away from support tongue 420.Preferably, the proximal portion 434 of electrodes 416 will remaincylindrical to facilitate the formation of a crimp-type electricalconnection between active electrodes 416 and lead wires 450 (see FIG.23). As shown in FIG. 26, cylindrical proximal portions 434 ofelectrodes 416 extend beyond spacer 418 by a slight distance of 0.1 mmto 0.4 mm. The semi-cylindrical configuration of distal electrodeportion 432 increases the electric field intensity and associatedcurrent density around the edges of ends 440, 442, as discussed above.Alternatively, active electrodes 416 may have any of the shapes andconfigurations described above or other configurations, such as squarewires, triangular shaped wires, U-shaped or channel shaped wires and thelike. In addition, the surface of active electrodes 416 may beroughened, e.g., by grit blasting, chemical or electrochemical etching,to further increase the electric field intensity and associated currentdensity around distal portions 432 of electrodes 416.

As shown in FIG. 24, each lead wire 450 terminates at a connector pin452 contained in a pin insulator block 454 within handpiece 408. Leadwires 450 are covered with an insulation layer (not shown), e.g.,Tefzel™, and sealed from the inner portion of support member 402 with anadhesive seal 457 (FIG. 22). In the preferred embodiment, each electrode416 is coupled to a separate source of voltage within power supply 28.To that end, connector pins 452 are removably coupled to matingreceptacles 456 within connector 410 to provide electrical communicationwith active electrodes 416 and power supply 28 (FIG. 1). Electricallyinsulated lead wires 458 connect receptacles 456 to the correspondingsources of voltage within power supply 28. The electrically conductivewall 414 of support member 402 serves as the return electrode, and issuitably coupled to one of the lead wires 450.

In an alternative embodiment, adjacent electrodes 416 may be connectedto the opposite polarity of source 28 so that current flows betweenadjacent active electrodes 416 rather than between active electrodes 416and return electrode 414. By way of example, FIG. 21B illustrates adistal portion of a planar ablation probe 400′ in which electrodes 416 aand 416 c are at one voltage polarity (i.e., positive) and electrodes416 b and 416 d are at the opposite voltage polarity (negative). When ahigh frequency voltage is applied between electrodes 416 a, 416 c andelectrodes 416 b, 416 d in the presence of electrically conductiveliquid, current flows between electrodes 416 a, 416 c and 416 b, 416 das illustrated by current flux lines 522′. Similar to the aboveembodiments, the opposite surface 420 of working end 404′ of probe 400′is generally atraumatic and electrically insulated from activeelectrodes 416 a, 416 b, 416 c and 416 d to minimize unwanted injury totissue in contact therewith.

In an exemplary configuration, each source of voltage includes a currentlimiting element or circuitry (not shown) to provide independent currentlimiting based on the impedance between each individual electrode 416and return electrode 414. The current limiting elements may be containedwithin the power supply 28, the lead wires 450, cable 34, handle 406, orwithin portions of the support member 402 distal to handle 406. By wayof example, the current limiting elements may include resistors,capacitors, inductors, or a combination thereof. Alternatively, thecurrent limiting function may be performed by (1) a current sensingcircuit which causes the interruption of current flow if the currentflow to the electrode exceeds a predetermined value and/or (2) animpedance sensing circuit which causes the interruption of current flow(or reduces the applied voltage to zero) if the measured impedance isbelow a predetermined value. In another embodiment, two or more of theelectrodes 416 may be connected to a single lead wire 450 such that allof the electrodes 416 are always at the same applied voltage relative toreturn electrode 414. Accordingly, any current limiting elements orcircuits will modulate the current supplied or the voltage applied tothe array of electrodes 416, rather than limiting their currentindividually, as discussed in the previous embodiment.

Referring to FIGS. 25–28, methods for ablating tissue structures withplanar ablation probe 400 according to the present invention will now bedescribed. In particular, exemplary methods for treating a diseasedmeniscus within the knee (FIGS. 29–31) and for removing soft tissuebetween adjacent vertebrae in the spine (FIG. 32) will be described. Inboth procedures, at least the working end 404 of planar ablation probe400 is introduced to a treatment site either by minimally invasivetechniques or open surgery. Electrically conductive liquid is deliveredto the treatment site, and voltage is applied from power supply 28between active electrodes 416 and return electrode 414. The voltage ispreferably sufficient to generate electric field intensities near activeelectrodes that form a vapor layer in the electrically conductiveliquid, and induce the discharge of energy from the vapor layer toablate tissue at the treatment site, as described in detail above.

Referring to FIG. 25, working end 404 and at least the distal portion ofsupport member 402 are introduced through a percutaneous penetration500, such as a cannula, into the arthroscopic cavity 502. The insertionof probe 400 is usually guided by an arthroscope (not shown) whichincludes a light source and a video camera to allow the surgeon toselectively visualize a zone within the knee joint. To maintain a clearfield of view and to facilitate the generation of a vapor layer, atransparent, electrically conductive irrigant 503, such as isotonicsaline, is injected into the treatment site either through a liquidpassage in support member 402 of probe 400, or through anotherinstrument. Suitable methods for delivering irrigant to a treatment siteare described in commonly assigned U.S. Pat. No. 5,697,281 filed on Jun.7, 1995, the contents of which are incorporated herein by reference.

In the example shown in FIG. 25, the target tissue is a portion of themeniscus 506 adjacent to and in close proximity with the articularcartilage 510, 508 which normally covers the end surfaces of the tibia512 and the femur 514, respectively. The articular cartilage 508, 510 isimportant to the normal functioning of joints, and once damaged, thebody is generally not capable of regenerating this critical lining ofthe joints. Consequently, it is desirable that the surgeon exerciseextreme care when treating the nearby meniscus 506 to avoid unwanteddamage to the articular cartilage 508, 510. The confined spaces 513between articular cartilage 508, 510 and meniscus 506 within the kneejoint are relatively narrow, typically on the order of about 1.0 mm to5.0 mm. Accordingly, the narrow, low profile working end 404 of ablationprobe 400 is ideally suited for introduction into these confined spaces513 to the treatment site. As mentioned previously, the substantiallyplanar arrangement of electrodes 416 and support tongue 420 (typicallyhaving a combined height of about 0.5 to 1.5 mm) allows the surgeon todeliver working end 404 of probe 400 into the confined spaces 513, whileminimizing contact with the articular cartilage 508, 510 (see FIG. 26).

As shown in FIG. 26, active electrodes 416 are disposed on one face ofworking end 404 of probe 400. Accordingly, a zone 520 of high electricfield intensity is generated on each electrode 416 on one face ofworking end 404 while the opposite side 521 of working end 404 isatraumatic with respect to tissue. In addition, the opposite side 521 isinsulated from electrodes 416 to minimize electric current from passingthrough this side 521 to the tissue (i.e., adjacent articular cartilage508). As shown in FIGS. 26, the bipolar arrangement of active electrodes416 and return electrode 414 causes electric current to flow along fluxlines 522 predominantly through the electrically conducting irrigant503, which envelops the tissue and working end 404 of ablation probe 400and provides an electrically conducting path between electrodes 416 andreturn electrode 414. As electrodes 416 are engaged with, or positionedin close proximity to, the target meniscus 506, the high electric fieldpresent at the electrode edges cause controlled ablation of the tissueby forming a vapor layer and inducing the discharge of energy therefrom.In addition, the motion of electrodes 416 relative to the meniscus 506(as shown by vector 523) causes tissue to be removed in a controlledmanner. The presence of the irrigant also serves to minimize theincrease in the temperature of the meniscus during the ablation processbecause the irrigant generally comes in contact with the treated tissueshortly after one of the electrodes 416 has been translated across thesurface of the tissue.

Referring now to FIG. 28, an exemplary method for removing soft tissue540 from the surfaces of adjacent vertebrae 542, 544 in the spine willnow be described. Removal of this soft tissue 540 is often necessary,for example, in surgical procedures for fusing or joining adjacentvertebrae together. Following the removal of tissue 540, the adjacentvertebrae 542, 544 are stabilized to allow for subsequent fusiontogether to form a single monolithic vertebra. As shown, the low-profileof working end 404 of probe 400 (i.e., thickness values as low as 0.2mm) allows access to and surface preparation of closely spacedvertebrae. In addition, the shaped electrodes 416 promote substantiallyhigh electric field intensities and associated current densities betweenactive electrodes 416 and return electrode 414 to allow for theefficient removal of tissue attached to the surface of bone withoutsignificantly damaging the underlying bone. The “non-active” insulatingside 521 of working end 404 also minimizes the generation of electricfields on this side 521 to reduce ablation of the adjacent vertebra 542.

The target tissue is generally not completely immersed in electricallyconductive liquid during surgical procedures within the spine, such asthe removal of soft tissue described above. Accordingly, electricallyconductive liquid will preferably be delivered into the confined spaces513 between adjacent vertebrae 542, 544 during this procedure. The fluidmay be delivered through a liquid passage (not shown) within supportmember 402 of probe 400, or through another suitable liquid supplyinstrument.

Other modifications and variations can be made to disclose embodimentswithout departing from the subject invention as defined in the followingclaims. For example, it should be clearly understood that the planarablation probe 400 described above may incorporate a single activeelectrode, rather than a plurality of such active electrodes asdescribed above in the exemplary embodiment. FIG. 27 illustrates aportion of a planar ablation probe according to the present inventionthat incorporates a single active electrode 416′ for generating highelectric field densities 550 to ablate a target tissue 552. Electrode416′ may extend directly from a proximal support member, as depicted inFIG. 31, or it may be supported on an underlying support tongue (notshown) as described in the previous embodiment. As shown, therepresentative single active electrode 416′ has a semi-cylindricalcross-section, similar to the electrodes 416 described above. However,the single electrode 416′ may also incorporate any of the abovedescribed configurations (e.g., square or star shaped solid wire) orother specialized configurations depending on the function of thedevice.

Referring now to FIGS. 29–31 an alternative electrode support member 500for a planar ablation probe 404 will be described in detail. As shown,electrode support member 500 preferably comprises a multilayer or singlelayer substrate 502 comprising a suitable high temperature, electricallyinsulating material, such as ceramic. The substrate 502 is a thin orthick film hybrid having conductive strips that are adhered to, e.g.,plated onto, the ceramic wafer. The conductive strips typically comprisetungsten, gold, nickel or equivalent materials. In the exemplaryembodiment, the conductive strips comprise tungsten, and they areco-fired together with the wafer layers to form an integral package. Theconductive strips are coupled to external wire connectors by holes orvias that are drilled through the ceramic layers, and plated orotherwise covered with conductive material.

In the representative embodiment, support member 500 comprises a singleceramic wafer having a plurality of longitudinal ridges 504 formed onone side of the wafer 502. Typically, the wafer 502 is green pressed andfired to form the required topography (e.g., ridges 504). A conductivematerial is then adhered to the ridges 504 to form conductive strips 506extending axially over wafer 502 and spaced from each other. As shown inFIG. 30, the conductive strips 506 are attached to lead wires 508 withinshaft 412 of the probe 404 to electrically couple conductive strips 506with the power supply 28 (FIG. 1). This embodiment provides a relativelylow profile working end of probe 404 that has sufficient mechanicalstructure to withstand bending forces during a surgical procedure.

FIGS. 34–36 illustrate another system and method for treating swollen orherniated intervertebral discs according to the present invention. Inthis procedure, an electrosurgical probe 700 comprises a long, thinshaft 702 (e.g., on the order of about 1 mm or less in diameter) thatcan be percutaneously introduced posteriorly through the patient's backdirectly into the spine. The probe shaft 702 will include one or moreactive electrode(s) 704 for applying electrical energy to tissues withinthe spine. The probe 700 may include one or more return electrodes 706,or the return electrode may be positioned on the patient's back as adispersive pad (not shown).

As shown in FIG. 34, the distal portion of shaft 702 is introducedposteriorly through a small percutaneous penetration into the annulus292 of the target intervertebral disc 290. To facilitate this process,the distal end of shaft 702 may taper down to a sharper point (e.g., aneedle), which can then be retracted to expose active electrode(s) 704.Alternatively, the active electrode(s) may be formed around the surfaceof the tapered distal portion of shaft 702 (not shown). In eitherembodiment, the distal end of shaft 702 is delivered through the annulus292 to the target nucleus pulposus 291, which may be herniated,extruded, non-extruded, or simply swollen. As shown in FIG. 35, highfrequency voltage is applied between active electrode(s) 704 and returnelectrode(s) 706 to heat the surrounding collagen to suitabletemperatures for contraction (i.e., typically about 55° C. to about 70°C.). As discussed above, this procedure may be accomplished with amonopolar configuration, as well. However, applicant has found that thebipolar configuration shown in FIGS. 34–36 provides enhanced control ofthe high frequency current, which reduces the risk of spinal nervedamage.

As shown in FIGS. 35 and 36, once the nucleus pulposus 291 has beensufficiently contracted to retract from impingement on a nerve or nerveroot, probe 700 is removed from the target site. In the representativeembodiment, the high frequency voltage is applied between active andreturn electrode(s) 704, 706 as the probe is withdrawn through theannulus 292. This voltage is sufficient to cause contraction of thecollagen fibers within the annulus 292, which allows the annulus 292 tocontract around the hole formed by probe 700, thereby improving thehealing of this hole. Thus, the probe 700 seals its own passage as it iswithdrawn from the disc.

FIGS. 37A to 39 illustrate systems and methods for treating and ablatingintervertebral discs according to the present invention. Electrosurgicalprobe 800 generally comprises a shaft 802 that can be percutaneouslyintroduced posteriorly (through the patient's back) into the spine. Theshaft 802 will include one or more active electrode(s) 804 for applyingelectrical energy to the intervertebral disc. The system may include oneor more return electrodes 806. The return electrode(s) 806 can bepositioned proximal of the active electrode(s) 804 on theelectrosurgical probe or on a separate instrument (not shown). Theablation probe 800 shown in FIG. 37A is configured to operate in thebipolar modality. In alternative embodiments, however, the returnelectrode 806 may be positioned on the patient's back as a dispersivepad (not shown) so as to operate in a monopolar modality.

In the exemplary embodiment shown in FIGS. 37A and 37B, the distal endof the shaft 802 is curved or bent to improve access to the disk beingtreated. The treatment surface 808 of the electrosurgical probe isusually curved or bent to an angle of about 10 degrees to 90 degreesrelative to the longitudinal axis of shaft 802, preferably about 15degrees to 60 degrees and more preferably about 15 degrees. Inalternative embodiments, the distal portion of shaft 802 comprises aflexible material which can be deflected relative to the longitudinalaxis of the shaft. Such deflection may be selectively induced bymechanical tension of a pull wire, for example, or by a shape memorywire that expands or contracts by externally applied temperaturechanges. A more complete description of this embodiment can be found inU.S. Pat. No. 5,697,909, the complete disclosure of which isincorporated herein by reference. Alternatively, the shaft 802 of thepresent invention may be bent by the physician to the appropriate angleusing a conventional bending tool or the like.

The active electrode(s) 804 typically extend from an active tissuetreatment surface of an electrode support member 810 of the probe shaft802. Opposite of the active electrodes 802 is a non-active insulatingside 812, which has an insulator 814 that is configured to protect thedura mater 816 and other non-target tissue, e.g., spinal cord 818. Theinsulator 814 minimizes the generation of electric fields on thenon-active side and reduces the electrical damage to the dura mater 816and spinal cord 818 during disc ablation. While the insulator 814 isshown opposite the active electrode array 804, it will be appreciatedthat the insulator 814 can be positioned completely around the probe, bepositioned around only portions of the probe, be along the sides of theactive electrode array, and the like.

The tissue treatment surface 808 and individual active electrodes 804will usually have dimensions within the ranges set forth above. In someembodiments, the active electrodes 804 can be disposed within or on aninsulating support member 810, as described above. In the representativeembodiment, the surface of the active electrodes 804 has a circularcross-sectional shape with a diameter in the range of about 1 mm to 30mm, usually about 2 mm to 20 mm. The individual active electrodes 802preferably extend outward from tissue treatment surface 808 by adistance of about 0.1 mm to 8 mm, usually about 0.2 mm to 4 mm.Applicant has found that this configuration increases the electric fieldintensities and associated current densities around active electrodes804 to facilitate the ablation of tissue as described in detail above.Of course, it will be recognized that the active electrodes may have avariety of different configurations. For example, instead of an array ofactive electrodes, a single active electrode may be used.

An exemplary method for ablating and removing at least a portion of thetarget intervertebral disc 290 will now be described. Removal of adegenerative or damaged disc is necessary, for example, in surgicalprocedures during placement of a cage, or the fusing or joining ofadjacent vertebrae together. Following the removal of the disc 290, theadjacent vertebrae 824 are stabilized to allow for subsequent fusiontogether to form a single monolithic vertebra. During such procedures itwould be preferable to protect the dura mater 816 and spinal cord 818from damage from the electrosurgical probe 800.

In use, the distal end of probe 800 is introduced into a treatment siteeither by minimally invasive techniques or open surgery. The distalportion of electrosurgical probe 800 can be introduced through apercutaneous penetration 826 e.g., via a camiula, into the body cavity828. The insertion of probe 800 is usually guided by an endoscope (notshown) which can include a light source and a video camera to allow thesurgeon to selectively visualize a zone within the vertebral column. Thedistal portion of shaft 802 can be introduced posteriorly through asmall percutaneous penetration into the annulus fibrosus 292 of thetarget intervertebral disc 290 (FIGS. 38 and 39).

To maintain a clear field of view and to facilitate the generation of avapor layer, a transparent, electrically conductive irrigant (notshown), such as isotonic saline, can be injected into the treatment siteeither through a liquid passage in probe 800, or through anotherinstrument. Suitable methods for delivering irrigant to a treatment siteare described in commonly assigned, U.S. Pat. No. 5,697,281 filed onJun. 7, 1995, the contents of which are incorporated herein byreference.

After (or during) introduction of the electrosurgical probe 800 into theintervertebral disc 290, an electrically conductive liquid 830 can bedelivered to the treatment site, and voltage can be applied from powersupply 28 between active electrodes 804 and return electrode 806 throughthe conductive fluid. The voltage is preferably sufficient to generateelectric field intensities near active electrodes 804 that form a vaporlayer in the electrically conductive liquid so as to induce a dischargeof energy from the vapor layer to ablate tissue at the treatment site,as described in detail above. As shaft 802 is moved through the spinaldisc 290, the insulator 814 can be positioned to engage the dura mater816 and protect the dura mater 816 (and spinal cord 818) from damagingelectrical current flow.

FIGS. 40 to 41 show yet another embodiment of the present invention. Theelectrosurgical probe 800 includes an aspiration lumen 832 foraspirating the target area and a fluid delivery lumen 834 for directingan electrically conductive fluid 830 to the target area. In someimplementations, the aspiration lumen 832 and the fluid delivery lumen834 are coupled together in an annular pattern along the exterior of theelectrosurgical probe. A distal end of the aspiration lumen 832typically ends proximal of the return electrode 806 while the distal endof the fluid delivery lumen 834 extends to a point adjacent the distalend of the electrosurgical probe 800. As shown in FIG. 41, the fluiddelivery lumen 834 preferably occupies a larger portion of the annularregion. In one specific embodiment, the fluid delivery lumen 834occupies approximately two-thirds of the annular region.

The electrosurgical probe may have a single active electrode 804 or anelectrode array distributed over a contact surface of a probe. In thelatter embodiment, the electrode array usually includes a plurality ofindependently current-limited and/or power-controlled active electrodesto apply electrical energy selectively to the target tissue whilelimiting the unwanted application of electrical energy to thesurrounding tissue and environment. In one specific configuration theelectrosurgical probe comprises 23 active electrodes. Of course, it willbe appreciated that the number, size, and configuration of the activeelectrodes may vary depending on the specific use of the electrosurgicalprobe (e.g. tissue contraction, tissue ablation, or the like).

The shaft 802 will usually house a plurality of wires or otherconductive elements axially therethrough to permit connection of activeelectrodes or electrode array 804 to a connector at the proximal end ofthe shaft (not shown). Each active electrode of an active electrodearray may be connected to a separate power source that is isolated fromthe other active electrodes. Alternatively, active electrodes 804 may beconnected to each other at either the proximal or distal ends of theprobe to form a single wire that couples to a power source.

The active electrode(s) 804 are typically supported by an electricallyinsulating electrode support member 836 that extends from theelectrosurgical probe 800. Electrode support member 836 typicallyextends from the distal end of shaft 802 about 1 mm to 20 mm. Electrodesupport member 836 typically comprises an insulating material (e.g., asilicone, ceramic, or glass material, such as alumina, zirconia and thelike) which could be formed at the time of manufacture in a flat,hemispherical or other shape according to the requirements of aparticular procedure.

In use, the electrosurgical probe 800 can be positioned adjacent thetarget tissue, as described above. When treating an intervertebral disc,the distal end of shaft 802 is typically delivered through the annulusto the nucleus pulposus 291, which may be herniated, extruded,non-extruded, or simply swollen. As shown in FIG. 42, high frequencyvoltage is applied between active electrode(s) 804 and returnelectrode(s) 806 to heat the surrounding collagen to suitabletemperatures for contraction (i.e., typically about 55° C. to about 70°C.) or ablation (i.e. typically less than 150° C.). As discussed above,this procedure may also be performed with a monopolar configuration.However, applicant has found that the bipolar configuration providesenhanced control of the high frequency current, which reduces the riskof spinal nerve damage.

In the exemplary embodiments, an electrically conductive fluid 830 isdelivered through fluid delivery lumen 834 to the target site. In theseembodiments, the high frequency voltage applied to the activeelectrode(s) is sufficient to vaporize the electrically conductive fluid(e.g., gel or saline) between the active electrode(s) and the tissue.Within the vaporized fluid, an ionized plasma is formed and chargedparticles (e.g., electrons) are accelerated towards the tissue to causethe molecular breakdown or disintegration of several cell layers of thetissue. This molecular dissociation is accompanied by the volumetricremoval of the tissue. Because the aspiration lumen 832 is placedproximal of the return electrode (and typically outside of theintervertebral disc 290), the aspiration lumen 832 typically removes theair bubbles from the spinal disc and leaves the disc tissue relativelyintact. Moreover, because the aspiration lumen 834 is spaced from thetarget area, the conductive fluid 830 is allowed to stay in the targetarea longer and the plasma can be created more aggressively.

FIGS. 43A to 43D show embodiments of the electrosurgical probe of thepresent invention which have a curved or steerable distal tip forimproving navigation of the electrosurgical probe 800 within the disc.Referring now to FIG. 43A, probe 800 comprises an electricallyconductive shaft 802, a handle 803 coupled to the proximal end of shaft802 and an electrically insulating support member 836 at the distal endof shaft 802. Probe 800 further includes an insulating sleeve 838 overshaft 802, and an exposed portion of shaft 802 that functions as thereturn electrode 806. In the representative embodiment, probe 800comprises a plurality of active electrodes 804 extending from the distalend of support member 836. As shown, return electrode 806 is spaced afurther distance from active electrodes 804 than in the embodimentsdescribed above. In this embodiment, the return electrode 806 is spaceda distance of about 2.0 mm to 50 mm, preferably about 5 mm to 25 mm. Inaddition, return electrode 806 has a larger exposed surface area than inprevious embodiments, having a length in the range of about 2.0 mm to 40mm, preferably about 5 mm to 20 mm. Accordingly, electric currentpassing from active electrodes 804 to return electrode 806 will follow acurrent flow path 840 that is further away from shaft 802 than in theprevious embodiments. In some applications, this current flow path 840results in a deeper current penetration into the surrounding tissue withthe same voltage level, and thus increased thermal heating of thetissue. As discussed above, this increased thermal heating may haveadvantages in some applications of treating disc or other spinaldefects. Typically, it is desired to achieve a tissue temperature in therange of about 60° C. to 100° C. to a depth of about 0.2 mm to 5 mm,usually about 1 mm to 2 mm. The voltage required for this thermaltreatment will depend in part on the electrode configuration, theconductivity of the tissue and of the milieu immediately surrounding theelectrodes, and the time period during which the voltage is applied.With the electrode configuration described in FIGS. 43A–43D, the voltagelevel for thermal heating will usually be in the range of about 20 voltsrms to 300 volts rms, preferably about 60 volts rms to 200 volts rms.The peak-to-peak voltages for thermal heating with a square wave formhaving a crest factor of about 2 are typically in the range of about 40to 600 volts peak-to-peak, preferably about 120 to 400 voltspeak-to-peak. The higher the voltage is within this range, the less timerequired for a given effect. If the voltage is too high, however, thesurface tissue may be vaporized, debulked or ablated, which is oftenundesirable.

As shown by the dotted lines in FIGS. 43A–43D, the distal tip 837 of theelectrosurgical probe 800 can have a pre-formed curvature or can besteered to a curved configuration so as to approximate the curvature ofthe inner surface 839 of the annulus (FIGS. 46A–B). In some embodiments,distal tip 837 is made of a shape memory material that can be shaped toapproximate the inside curvature of the annulus. In other embodiments,distal tip 837 of the electrosurgical probe 800 is steerable ordeflectable by the user. The flexible shaft and steerable distal tip maybe combined with pull wires, shape memory actuators, heat actuatedmaterials, or other conventional or proprietary mechanisms for effectingselective deflection of the distal tip of the shaft to facilitatepositioning of the electrode array relative to a target tissue. A usercan track the position of the steerable distal tip using fluoroscopy,optical fibers, transducers positioned on the probe, or the like.

In some embodiments, the electrosurgical probe 800 may include adispersive return electrode 842 (FIG. 44) for operating the apparatus inmonopolar mode. In this embodiment, the power supply 28 will typicallyinclude a switch, e.g., a foot pedal 843, for switching between themonopolar and bipolar modes. The system will switch between an ablationmode, where the dispersive pad 842 is deactivated and voltage is appliedbetween active and return electrodes 804, 806, and a subablation orthermal heating mode, where the active electrode(s) 804 are deactivatedand voltage is applied between the dispersive pad 842 and the returnelectrode 806. In the subablation mode, a lower voltage is typicallyapplied and the return electrode 806 functions as the active electrodeto provide thermal heating and/or coagulation of tissue surroundingreturn electrode 806. A more complete description of the use of thedispersive return electrode is described in co-pending U.S. patentapplication Ser. No. 09/316,472, filed May 21, 1999, the completedisclosure of which is incorporated herein by reference.

FIG. 43B illustrates yet another embodiment of the present invention. Asshown, electrosurgical probe 800 comprises an electrode assembly havingone or more active electrode(s) 804 and a proximally spaced returnelectrode 806 as in previous embodiments. Return electrode 806 istypically spaced about 0.5 mm to 25 mm, preferably 1.0 mm to 5.0 mm fromthe active electrode(s) 804, and has an exposed length of about 1 mm to20 mm. In addition, the electrode assembly can include two additionalelectrodes 844, 846 spaced axially on either side of return electrode806. Electrodes 844, 846 are typically spaced about 0.5 mm to 25 mm,preferably about 1 mm to 5 mm from return electrode 806. In therepresentative embodiment, the additional electrodes 844, 846 areexposed portions of shaft 802, and the return electrode 806 iselectrically insulated from shaft 802 such that a voltage difference maybe applied between electrodes 844, 846 and electrode 806. In thisembodiment, probe 800 may be used in at least two different modes, anablation mode and a subablation or thermal heating mode. In the ablationmode, voltage is applied between active electrode(s) 804 and returnelectrode 806 in the presence of electrically conductive fluid, asdescribed above. In the ablation mode, electrodes 844, 846 aredeactivated. In the thermal heating or coagulation mode, activeelectrode(s) 804 are deactivated and a voltage difference is appliedbetween electrodes 844, 846 and electrode 806 such that a high frequencycurrent 840 flows therebetween, as shown in FIG. 43B. In the thermalheating mode, a lower voltage is typically applied such that the voltageis below the threshold for plasma formation and ablation, but sufficientto cause some thermal damage to the tissue immediately surrounding theelectrodes without vaporizing or otherwise debulking this tissue so thatthe current 840 provides thermal heating and/or coagulation of tissuesurrounding electrodes 804, 844, 846.

FIG. 43C illustrates another embodiment of probe 800 incorporating anelectrode assembly having one or more active electrode(s) 804 and aproximally spaced return electrode 806 as in previous embodiments.Return electrode 806 is typically spaced about 0.5 mm to 25 mm,preferably 1.0 mm to 5.0 mm from the active electrode(s) 804, and has anexposed length of about 1 mm to 20 mm. In addition, the electrodeassembly includes a second active electrode 848 separated from returnelectrode 806 by an electrically insulating spacer 382. In thisembodiment, handle 803 includes a switch 850 for toggling probe 800between at least two different modes, an ablation mode and a subablationor thermal heating mode. In the ablation mode, voltage is appliedbetween active electrode(s) 804 and return electrode 806 in the presenceof electrically conductive fluid, as described above. In the ablationmode, electrode 848 is deactivated. In the thermal heating orcoagulation mode, active electrode(s) 804 may be deactivated and avoltage difference is applied between electrode 848 and electrode 806such that a high frequency current 840 flows therebetween.Alternatively, active electrode(s) 804 may not be deactivated as thehigher resistance of the smaller electrodes (active electrodes 804) mayautomatically send the electric current to electrode 848 without havingto physically decouple electrode(s) 804 from the circuit. In the thermalheating mode, a lower voltage is typically applied, i.e. a voltage belowthe threshold for plasma formation and ablation, but sufficient to causesome thermal damage to the tissue immediately surrounding the electrodeswithout vaporizing or otherwise debulking this tissue so that thecurrent 840 provides thermal heating and/or coagulation of tissuesurrounding electrodes 804, 848.

FIG. 43D illustrates yet another embodiment of the invention designedfor channeling through tissue and creating lesions therein to treat theinterior tissue of intervertebral discs. As shown, probe 800 is similarto the probe in FIG. 43C having a return electrode 806 and a third,coagulation electrode 848 spaced proximally from the return electrode806. In this embodiment, active electrode 804 comprises a singleelectrode wire extending distally from insulating support member 836. Ofcourse, the active electrode 804 may have a variety of configurations toincrease the current densities on its surfaces, e.g., a conical shapetapering to a distal point, a hollow cylinder, loop electrode and thelike. This embodiment includes a proximal support member 852. In therepresentative embodiment, support members 836 and 852 are constructedof inorganic material, such as a ceramic, a glass, a silicone, and thelike. The proximal support member 852 may also comprise a moreconventional organic material as this support member 852 will generallynot be in the presence of a plasma that would otherwise etch or wearaway an organic material.

The probe 800 in FIG. 43D does not include a switching element. In thisembodiment, all three electrodes are activated when the power supply isactivated. The return electrode 806 has an opposite polarity from theactive and coagulation electrodes 804, 848 such that current 840 flowsfrom the latter electrodes to the return electrode 806 as shown. In thepreferred embodiment, the electrosurgical system includes a voltagereduction element or a voltage reduction circuit for reducing thevoltage applied between the coagulation electrode 848 and returnelectrode 806. The voltage reduction element allows the power supply 28(FIG. 1) to, in effect, apply two different voltages simultaneously totwo different electrodes. Thus, for channeling through tissue, theoperator may apply a voltage sufficient to provide ablation of thetissue at the tip of the probe (i.e., tissue adjacent to the activeelectrode 804). At the same time, the voltage applied to the coagulationelectrode 848 will be insufficient to ablate tissue. For thermal heatingor coagulation of tissue, for example, the voltage reduction elementwill serve to reduce a voltage from about 100 to 300 volts rms down toabout 45 to 90 volts rms, wherein the latter range provides a suitablevoltage for coagulation of tissue without ablation (e.g., withoutmolecular dissociation) of the tissue.

In the representative embodiment, the voltage reduction element is acapacitor (not shown) coupled to the power supply and coagulationelectrode 848. The capacitor usually has a capacitance of about 200 pFto 500 pF (at 500 volts) and preferably about 300 pF to 350 pF (at 500volts). Of course, the capacitor may be located in other places withinthe system, such as in, or distributed along the length of, the cable,the generator, the connector, etc. In addition, it will be recognizedthat other voltage reduction elements, such as diodes, transistors,inductors, resistors, capacitors or combinations thereof, may be used inconjunction with the present invention. For example, the probe 800 mayinclude a coded resistor (not shown) that is constructed to lower thevoltage applied between the return and coagulation electrodes 806, 848.In addition, electrical circuits may be employed for this purpose.

Of course, for some procedures, the probe will typically not require avoltage reduction element. Alternatively, the probe may include avoltage increasing element or circuit, if desired. Alternatively oradditionally, cable 22 (FIG. 1) that couples power supply 28 to probe800 may be used as a voltage reduction element. The cable has aninherent capacitance that can be used to reduce the power supply voltageif the cable is placed into the electrical circuit between the powersupply, the active electrodes and the return electrode. In thisembodiment, the cable 22 may be used alone, or in combination with oneof the voltage reduction elements discussed above, e.g., a capacitor.Further, it should be noted that the present invention can be used witha power supply that is adapted to apply two different voltages withinthe selected range for treatment of tissue. In this embodiment, avoltage reduction element or circuitry may not be desired.

In use, the electrosurgical instruments of FIGS. 43A–43D can be used totreat the tissue within the disc 290. In particular, the electrosurgicalinstrument 800 can be used to treat damaged discs (e.g., herniated,bulging, fissured, protruding, or the like), denervate selected nervesembedded in the annulus, cauterize granulation tissue that is ingrowninto the annulus, seal fissures along the inner surface of the annulus,and the like. Preferably, the electrosurgical probe 800 can achievethese results in a minimally destructive manner so as to maintain thewater content and tissue mass within the disc. Of course, the presentinvention can also be adapted to ablate tissue, to shrink tissue, todecrease the mass of tissue, or to reduce the water content of the disc.

In preferred embodiments, the electrosurgical probe 800 minimizesablation of the nucleus pulposus 291 by moving along an inner surface ofthe annulus 292. Accordingly, after the distal tip of theelectrosurgical probe is inserted into the disc 290 (FIG. 45), thedistal tip 837 can be steered along the interface between the annulus292 and nucleus pulposus 291.

Referring now to FIG. 45, in some methods the physician positions activeelectrode 804 adjacent to the tissue surface to be treated (e.g., anintervertebral disc). The power supply is activated to provide anablation voltage between active and return electrodes 804, 806 and acoagulation or thermal heating voltage between coagulation and returnelectrodes 806, 848. An electrically conductive fluid can then beprovided around active electrode 804, and in the junction between theactive and return electrodes 804, 806 to provide a current flow paththerebetween. This may be accomplished in a variety of manners, asdiscussed above. The active electrode 804 is then advanced through thespace left by the ablated tissue to form a channel in the disc. Duringablation, the electric current between the coagulation and returnelectrode is typically insufficient to cause any damage to the surfaceof the tissue as these electrodes pass through the tissue surface intothe channel created by active electrode 804. Once the physician hasformed the channel to the appropriate depth, he or she will ceaseadvancement of the active electrode, and will either hold the instrumentin place for approximately 5 seconds to 30 seconds, or can immediatelyremove the distal tip of the instrument from the channel (see detaileddiscussion of this below). In either event, when the active electrode isno longer advancing, it will eventually stop ablating tissue.

Prior to entering the channel formed by the active electrode 804, anopen circuit exists between return and coagulation electrodes 806, 848.Once coagulation electrode 848 enters this channel, electric currentwill flow from coagulation electrode 848, through the tissue surroundingthe channel, to return electrode 806. This electric current will heatthe tissue immediately surrounding the channel to coagulate any severedvessels at the surface of the channel. If the physician desires, theinstrument may be held within the channel for a period of time to createa lesion around the channel.

In an exemplary embodiment, once the distal tip 837 of theelectrosurgical probe 800 has channeled through the annulus fibrosus292, the distal tip 837 can be steered or deflected so as to move alongthe inner surface of the annulus fibrosus 292. As shown in FIGS. 46A and46B, the electrosurgical device is advanced into an intervertebral disc290, and the physician can simultaneously steer the distal tip 237 fromthe proximal end of the electrosurgical device (not shown). As notedabove, the distal end of the electrosurgical device preferably issteered or deflected around the inner surface 839 of the annulusfibrosus 292. The physician can use fluoroscopy to monitor the positionand movement of the distal end of the probe. Alternatively, the surgeonmay insert an imaging device or transducer directly into the disc tomonitor the position of electrodes 804, 806, and 848. The imaging device(not shown) can be positioned on the electrosurgical probe or it can beon a separate instrument.

In other embodiments, instead of a steerable distal tip 837, the distaltip of the electrosurgical probe 800 can be composed of a shape-memorymaterial that can be pre-shaped to have the approximate curve of theinner surface of the annulus 292. The shape-memory tip can be biased toa pre-bent curved configuration, such that in the absence of astraightening force (e.g., within the annulus, within a tube, or thelike) the distal tip will bias to the curved configuration. For example,after an operating corridor has been created to the target site,electrosurgical probe 800 can be moved adjacent the outer surface of theannulus fibrosus 292 (FIGS. 12–15). The active electrode 804 can channelthrough the tough annulus fibrosus 292, as described above. Once thedistal tip 837 enters the nucleus pulposus 291, the distal tip will nolonger be constrained in the substantially straight configuration by thetough, annulus fibrosus 292 and the distal tip will bias to its pre-bentcurved configuration. As the electrosurgical device is advanced into thedisc 290, the biased distal tip encourages the electrosurgicalinstrument to follow the curved inner surface 839 of the annulusfibrosus 292.

As described in detail above, once electrosurgical probe 800 has beensteered to the target position, the high frequency voltage can bedelivered between the active electrode(s) and return electrode(s) in abipolar mode or monopolar mode to treat inner surface 839 of annulusfibrosus 292. In some embodiments, an electrically conductive fluid,such as isotonic saline, can be delivered to the active electrode. Asnoted above, in procedures requiring ablation of tissue, the tissue isremoved by molecular dissociation or disintegration processes. In theseembodiments, the high frequency voltage applied to the activeelectrode(s) is sufficient to vaporize the electrically conductive fluidbetween the active electrode(s) and the tissue. Within the vaporizedfluid, an ionized plasma is formed and charged particles (e.g.,electrons) cause the molecular breakdown or disintegration of the tissueto a depth of perhaps several cell layers. This molecular dissociationis accompanied by the volumetric removal of the tissue. The moleculardissociation process can be precisely controlled to target specifictissue structures or layers, thereby minimizing damage and necrosis tonon-target tissue. In monopolar embodiments, the conductive fluid needonly be sufficient to surround the active electrode and to provide alayer of fluid between the active electrode and the tissue. In bipolarembodiments, the conductive fluid preferably generates a current flowpath between the active electrode(s) and the return electrode(s).

Depending on the procedure, the inner surface 839 of annulus 292 can beablated, contracted, coagulated, sealed, or the like. For example, thehigh frequency voltage can be used to denervate the pain receptors in afissure in the annulus fibrosus, deactivate the neurotransmitters,deactivate heat-sensitive enzymes, denervate nerves embedded in the wallof the annulus fibrosus, ablate granulation tissue in the annulusfibrosus, shrink collagen in the annulus fibrosus, or the like.

Other modifications and variations can be made to disclose embodimentswithout departing from the subject invention as defined in the followingclaims. For example, it should be noted that the invention is notlimited to an electrode array comprising a plurality of activeelectrodes. Certain embodiments of the invention could utilize aplurality of return electrodes, e.g., in a bipolar array or the like. Inaddition, depending on other conditions, such as the peak-to-peakvoltage, electrode diameter, etc., a single active electrode may besufficient to contract collagen tissue, ablate tissue, or the like.

In addition, the active and return electrodes may both be located on adistal tissue treatment surface adjacent to each other. The active andreturn electrodes may be located in active/return electrode pairs, orone or more return electrodes may be located on the distal tip togetherwith a plurality of electrically isolated active electrodes. Theproximal return electrode may or may not be employed in theseembodiments. For example, if it is desired to maintain the current fluxlines around the distal tip of the probe, the proximal return electrodewill not be desired.

There now follows a description, with reference to FIGS. 47A–50B, of anelectrosurgical probe having a curved shaft, according to additionalembodiments of the invention. FIG. 47A is a side view of anelectrosurgical probe 900, including a shaft 902 having a distal endportion 902 a and a proximal end portion 902 b. An active electrode 910is disposed on distal end portion 902 a. Although only one activeelectrode is shown in FIG. 26A, embodiments having a plurality of activeelectrodes are also within the scope of the invention. Probe 900 furtherincludes a handle 904 which houses a connection block 906 for couplingelectrodes, e.g. active electrode 910, thereto. Connection block 906includes a plurality of pins 908 adapted for coupling probe 900 to apower supply unit, e.g. power supply 28 (FIG. 1). FIG. 47A also shows afirst curve 924 and a second curve 926 located at shaft distal endportion 902 a, wherein second curve 926 is proximal to first curve 924.First curve 924 and second curve 926 may be separated by a linear (i.e.straight, or non-curved), or substantially linear, inter-curve portion925 of shaft 902.

FIG. 47B is a side view of shaft distal end portion 902 a within arepresentative introducer device or needle 928 having an inner diameterD. Shaft distal end portion 902 a includes first curve 924 and secondcurve 926 separated by inter-curve portion 925. In one embodiment, shaftdistal end portion 902a includes a linear or substantially linearproximal portion 901 extending from proximal end portion 902 b to secondcurve 926, a linear or substantially linear inter-curve portion 925between first and second curves 924, 926, and a linear or substantiallylinear distal portion 909 between first curve 924 and the distal tip ofshaft 902 (the distal tip is represented in FIG. 47B as an electrodehead 911). When shaft distal end portion 902 a is located withinintroducer needle 928, first curve 924 subtends a first angle ∀ to theinner surface of needle 928, and second curve 926 subtends a secondangle ∃ to inner surface 932 of needle 928. (In the situation shown inFIG. 47B, needle inner surface 932 is essentially parallel to thelongitudinal axis of shaft proximal end portion 902 b (FIG. 47A).) Inone embodiment, shaft distal end portion 902 a is designed such that theshaft distal tip occupies a substantially central transverse locationwithin the lumen of introducer needle 928 when shaft distal end portion902 a is translated axially with respect to introducer needle 928. Thus,as shaft distal end portion 902 a is advanced through the distal openingof needle 928 (FIGS. 30B, 31B), and then retracted back into the distalopening, the shaft distal tip will always occupy a transverse locationtowards the center of introducer needle 928 (even though the tip may becurved or biased away from the longitudinal axis of shaft 902 and needle928 upon its advancement past the distal opening of introducer needle928). In one embodiment, shaft distal end portion 902 a is flexible andhas a configuration which requires shaft distal end portion 902 a bedistorted in the region of at least second curve 926 by application of alateral force imposed by inner wall 932 of introducer needle 928 asshaft distal end portion 902 a is introduced or retracted into needle928. In one embodiment, first curve 924 and second curve 926 are in thesame plane relative to the longitudinal axis of shaft 902, and first andsecond curves 924, 926 are in opposite directions.

The “S-curve” configuration of shaft 902 shown in FIGS. 47A–C allows thedistal end or tip of a device to be advanced or retracted through needledistal end 928 a and within the lumen of needle 928 without the distalend or tip contacting introducer needle 928. Accordingly, this designallows a sensitive or delicate component to be located at the distal tipof a device, wherein the distal end or tip is advanced or retractedthrough a lumen of an introducer instrument comprising a relatively hardmaterial (e.g., an introducer needle comprising stainless steel). Thisdesign also allows a component located at a distal end or tip of adevice to be constructed from a relatively soft material, and for thecomponent located at the distal end or tip to be passed through anintroducer instrument comprising a hard material without risking damageto the component comprising a relatively soft material.

The “S-curve” design of shaft distal end portion 902 a allows the distaltip (e.g., electrode head 911) to be advanced and retracted through thedistal opening of needle 928 while avoiding contact between the distaltip and the edges of the distal opening of needle 928. (If, for example,shaft distal end portion 902 a included only a single curve, the distaltip would ordinarily come into contact with needle distal end 928 a asshaft 902 is retracted into the lumen of needle 928.) In preferredembodiments, the length L2 of distal portion 909 and the angle ∀ betweendistal portion 909 and needle inner surface 932 928, when shaft distalend portion 902 a is compressed within needle 928, are selected suchthat the distal tip is substantially in the center of the lumen ofneedle 928, as shown in FIG. 47B. Thus, as the length L2 increases, theangle ∀ will decrease, and vice versa. The exact values of length L2 andangle ∀ will depend on the inner diameter, D of needle 928, the innerdiameter, d of shaft distal end portion 902 a, and the size of the shaftdistal tip.

The presence of first and second curves, 924, 926 provides a pre-definedbias in shaft 902. In addition, in one embodiment shaft distal endportion 902 a is designed such that at least one of first and secondcurves 924, 926 are compressed to some extent as shaft distal endportion 902 a is retracted into the lumen of needle 928. Accordingly,the angle of at least one of curves 924, 926 may be changed when distalend portion 902 a is advanced out through the distal opening ofintroducer needle 928, as compared with the corresponding angle whenshaft distal end portion is completely retracted within introducerneedle 928. For example, FIG. 47C shows shaft 902 of FIG. 47B free fromintroducer needle 928, wherein first and second curves 924, 926 areallowed to adopt their natural or uncompressed angles ∀′ and ∃′,respectively, wherein ∃′ is typically equal to or greater than ∃. Angle∀′ may be greater than, equal to, or less than angle ∀. Angle ∃′ issubtended by inter-curve portion 925 and proximal portion 901. Whenshaft distal end portion 902 a is unrestrained by introducer needle 928,proximal portion 901 approximates the longitudinal axis of shaft 902.Angle ∀′ is subtended between linear distal portion 909 and a line drawnparallel to proximal portion 901. Electrode head 911 is omitted fromFIG. 47C for the sake of clarity.

The principle described above with reference to shaft 902 and introducerneedle 928 may equally apply to a range of other medical devices. Thatis to say, the “S-curve” configuration of the invention may be includedas a feature of any medical system or apparatus in which a medicalinstrument may be axially translated or passed within an introducerdevice. In particular, the principle of the “S-curve” configuration ofthe invention may be applied to any apparatus wherein it is desired thatthe distal end of the medical instrument does not contact or impingeupon the introducer device as the medical instrument is advanced from orretracted into the introducer device. The introducer device may be anyapparatus through which a medical instrument is passed. Such medicalsystems may include, for example, a catheter, a cannula, an endoscope,and the like.

When shaft 902 is advanced distally through the needle lumen to a pointwhere second curve 926 is located distal to needle distal end 928 a, theshaft distal tip is deflected from the longitudinal axis of needle 928.The amount of this deflection is determined by the relative size ofangles ∃′ and ∀′, and the relative lengths of L1 and L2. The amount ofthis deflection will in turn determine the size of a channel or lesion(depending on the application) formed in a tissue treated by electrodehead 911 when shaft 902 is rotated circumferentially with respect to thelongitudinal axis of probe 900.

As a result of the pre-defined bias in shaft 902, shaft distal endportion 902a will contact a larger volume of tissue than a linear shafthaving the same dimensions. In addition, in one embodiment thepre-defined bias of shaft 902 allows the physician to guide or steer thedistal tip of shaft 902 by a combination of axial movement of needledistal end 928 a and the inherent curvature at shaft distal end portion902 a of probe 900.

Shaft 902 preferably has a length in the range of from about 4 to 30 cm.In one aspect of the invention, probe 900 is manufactured in a range ofsizes having different lengths and/or diameters of shaft 902. A shaft ofappropriate size can then be selected by the surgeon according to thebody structure or tissue to be treated and the age or size of thepatient. In this way, patients varying in size from small children tolarge adults can be accommodated. Similarly, for a patient of a givensize, a shaft of appropriate size can be selected by the surgeondepending on the organ or tissue to be treated, for example, whether anintervertebral disc to be treated is in the lumbar spine or the cervicalspine. For example, a shaft suitable for treatment of a disc of thecervical spine may be substantially smaller than a shaft for treatmentof a lumbar disc. For treatment of a lumbar disc in an adult, shaft 902is preferably in the range of from about 15 to 20 cm. For treatment of acervical disc, shaft 902 is preferably in the range of from about 4 toabout 15 cm.

The diameter of shaft 902 is preferably in the range of from about 0.5to about 2.5 mm, and more preferably from about 1 to 1.5 mm. First curve924 is characterized by a length L1, while second curve 926 ischaracterized by a length L2 (FIG. 47B). Inter-curve portion 925 ischaracterized by a length L3, while shaft 902 extends distally fromfirst curve 924 a length L4. In one embodiment, L2 is greater than L1.Length L1 may be in the range of from about 0.5 to about 5 mm, while L2may be in the range of from about 1 to about 10 mm. Preferably, L3 andL4 are each in the range of from about 1 to 6 mm.

FIG. 48A is a side view of electrosurgical probe 900 showing details ofshaft distal end portion 902 a including an active electrode head 911 ofactive electrode 910 (the latter not shown in FIG. 48A), according toone embodiment of the invention. Distal end portion 902 a includes aninsulating collar or spacer 916 proximal to active electrode head 911,and a return electrode 918 proximal to collar 916. A first insulatingsleeve (FIG. 48B) may be located beneath return electrode 918. A secondinsulating jacket or sleeve 920 may extend proximally from returnelectrode 918. Second insulating sleeve 920 serves as an electricalinsulator to inhibit current flow into non-target tissue. In a currentlypreferred embodiment, probe 900 further includes a shield 922 extendingproximally from second insulating sleeve 920. Shield 922 may be formedfrom a conductive metal such as stainless steel, and the like. Shield922 functions to decrease the amount of leakage current passing fromprobe 900 to a patient or a user (e.g., surgeon). In particular, shield922 decreases the amount of capacitive coupling between return electrode918 and an introducer needle 928 (FIG. 50A).

In this embodiment, electrode head 911 includes an apical spike 911 aand an equatorial cusp 911 b. Electrode head 911 exhibits a number ofadvantages as compared with, for example, an electrosurgical probehaving a blunt, globular, or substantially spherical active electrode.In particular, electrode head 911 provides a high current density atapical spike 911 a and cusp 911 b. In turn, high current density in thevicinity of an active electrode is advantageous in the generation of aplasma; and, as is described fully hereinabove, generation of a plasmain the vicinity of an active electrode is fundamental to ablation oftissue with minimal collateral thermal damage according to certainembodiments of the instant invention. Electrode head 911 provides anadditional advantage, in that the sharp edges of cusp 911 b, and moreparticularly of apical spike 911 a, facilitate movement and guiding ofhead 911 into fresh tissue during surgical procedures, as describedfully hereinbelow. In contrast, an electrosurgical probe having a bluntor rounded apical electrode is more likely to follow a path of leastresistance, such as a channel which was previously ablated withinnucleus pulposus tissue. Although certain embodiments of the inventiondepict head 911 as having a single apical spike, other shapes for theapical portion of active electrode 910 are also within the scope of theinvention.

FIG. 48B is a longitudinal cross-sectional view of distal end portion902 a of shaft 902. Apical electrode head 911 is in communication with afilament 912. Filament 912 typically comprises an electricallyconductive wire encased within a first insulating sleeve 914. Firstinsulating sleeve 914 comprises an insulator, such as various syntheticpolymeric materials. An exemplary material from which first insulatingsleeve 914 may be constructed is a polyimide. First insulating sleeve914 may extend the entire length of shaft 902 proximal to head 911. Aninsulating collar or spacer 916 is disposed on the distal end of firstinsulating sleeve 914, adjacent to electrode head 911. Collar 916preferably comprises a material such as a glass, a ceramic, or silicone.The exposed portion of first insulating sleeve 914 (i.e., the portionproximal to collar 916) is encased within a cylindrical return electrode918. Return electrode 918 may extend proximally the entire length ofshaft 902. Return electrode 918 may comprise an electrically conductivematerial such as stainless steel, tungsten, platinum or its alloys,titanium or its alloys, molybdenum or its alloys, nickel or its alloys,and the like. A proximal portion of return electrode 918 is encasedwithin a second insulating sleeve 920, so as to provide an exposed bandof return electrode 918 located distal to second sleeve 920 and proximalto collar 916. Second sleeve 920 provides an insulated portion of shaft920 which facilitates handling of probe 900 by the surgeon during asurgical procedure. A proximal portion of second sleeve 920 is encasedwithin an electrically conductive shield 922. Second sleeve 920 andshield 922 may also extend proximally for the entire length of shaft902.

FIG. 49A shows distal end portion 902 a of shaft 902 extended distallyfrom an introducer needle 928, according to one embodiment of theinvention. Introducer needle 928 may be used to conveniently introduceshaft 902 into tissue, such as the nucleus pulposus of an intervertebraldisc. In this embodiment, due to the curvature of shaft distal end 902a, when shaft 902 is extended distally beyond introducer needle 928,head 911 is displaced laterally from the longitudinal axis of introducerneedle 928. However, as shown in FIG. 49B, as shaft 902 is retractedinto introducer needle 928, head 911 assumes a substantially centraltransverse location within lumen 930 (see also FIG. 50B) of introducer928. Such re-alignment of head 911 with the longitudinal axis ofintroducer 928 is achieved by specific design of the curvature of shaftdistal end 902 a, as accomplished by the instant inventors. In thismanner, contact of various components of shaft distal end 902 a (e.g.,electrode head 911, collar 916, return electrode 918) is prevented,thereby not only facilitating extension and retraction of shaft 902within introducer 928, but also avoiding a potential source of damage tosensitive components of shaft 902.

FIG. 50A shows a side view of shaft 902 in relation to an inner wall 932of introducer needle 928 upon extension or retraction of electrode head911 from, or within, introducer needle 928. Shaft 902 is located withinintroducer 928 with head 911 adjacent to introducer distal end 928 a(FIG. 50B). Under these circumstances, curvature of shaft 902 may causeshaft distal end 902 a to be forced into contact with introducer innerwall 932, e.g., at a location of second curve 926. Nevertheless, due tothe overall curvature of shaft 902, and in particular the nature andposition of first curve 924 (FIGS. 47A–B), head 911 does not contactintroducer distal end 928 a.

FIG. 50B shows an end view of electrode head 911 in relation tointroducer needle 928 at a point during extension or retraction of shaft902, wherein head 911 is adjacent to introducer distal end 928 a (FIGS.49B, 50B). In this situation, head 911 occupies a substantially centraltransverse location within lumen 930 of introducer 928. Therefore,contact between head 911 and introducer 928 is avoided, allowing shaftdistal end 902 a to be extended and retracted repeatedly withoutsustaining any damage to shaft 902.

FIG. 51A shows shaft proximal end portion 902 b of electrosurgical probe900, wherein shaft 902 includes a plurality of depth markings 903 (shownas 903 a–f in FIG. 51A). In other embodiments, other numbers andarrangements of depth markings 903 may be included on shaft 902. Forexample, in certain embodiments, depth markings may be present along theentire length of shield 922, or a single depth marking 903 may bepresent at shaft proximal end portion 902 b. Depth markings serve toindicate to the surgeon the depth of penetration of shaft 902 into apatient's tissue, organ, or body, during a surgical procedure. Depthmarkings 903 may be formed directly in or on shield 922, and maycomprise the same material as shield 922. Alternatively, depth markings903 may be formed from a material other than that of shield 922. Forexample, depth markings may be formed from materials which have adifferent color and/or a different level of radiopacity, as comparedwith material of shield 922. For example, depth markings may comprise ametal, such as tungsten, gold, or platinum oxide (black), having a levelof radiopacity different from that of shield 922. Such depth markingsmay be visualized by the surgeon during a procedure performed underfluoroscopy. In one embodiment, the length of introducer needle 928 andshaft 902 are selected to limit the range of shaft distal end 902 abeyond the distal tip of introducer needle 928.

FIG. 51B shows a probe 900, wherein shaft 902 includes a mechanical stop905. Preferably, mechanical stop 905 is located at shaft proximal endportion 902 b. Mechanical stop 905 limits the distance to which shaftdistal end 902 a can be advanced through introducer 928 by makingmechanical contact with a proximal end 928 b of introducer 928.Mechanical stop 905 may be a rigid material or structure affixed to, orintegral with, shaft 902. Mechanical stop 905 also serves to monitor thedepth or distance of advancement of shaft distal end 902 a throughintroducer 928, and the degree of penetration of distal end 902 a into apatient's tissue, organ, or body. In one embodiment, mechanical stop 905is movable on shaft 902, and stop 905 includes a stop adjustment unit907 for adjusting the position of stop 905 and for locking stop 905 at aselected location on shaft 902.

FIG. 52A schematically represents a normal intervertebral disc 290 inrelation to the spinal cord 818, the intervertebral disc having an outerannulus fibrosus 292 enclosing an inner nucleus pulposus 291. Thenucleus pulposus is a relatively soft tissue comprising proteins andhaving a relatively high water content, as compared with the harder,more fibrous annulus fibrosus. FIGS. 52B–D each schematically representan intervertebral disc having a disorder which can lead to discogenicpain, for example due to compression of a nerve root by a distortedannulus fibrosus. Thus, FIG. 52B schematically represents anintervertebral disc exhibiting a bulge or protrusion of the nucleuspulposus and a concomitant distortion of the annulus fibrosus. Thecondition depicted in FIG. 52B clearly represents a containedherniation, which can result in severe and often debilitating pain. FIG.52C schematically represents an intervertebral disc exhibiting aplurality of fissures 1106 within the annulus fibrosus, again withconcomitant distortion of the annulus fibrosus. Such annular fissuresmay be caused by excessive pressure exerted by the nucleus pulposus onthe annulus fibrosus. Excessive pressure within the nucleus pulposustends to intensify disc disorders associated with the presence of suchfissures. FIG. 52D schematically represents an intervertebral discexhibiting fragmentation of the nucleus pulposus and a concomitantdistortion of the annulus fibrosus. In this situation, over time, errantfragment 291′ of the nucleus pulposus tends to dehydrate and to diminishin size, often leading to a decrease in discogenic pain over an extendedperiod of time (e.g., several months). For the sake of clarity, eachFIGS. 52B, 52C, 52D shows a single disorder. However, in practice morethan one of the depicted disorders may occur in the same disc.

Many patients suffer from discogenic pain resulting, for example, fromconditions of the type depicted in FIGS. 52B–D. However, only a smallpercentage of such patients undergo laminotomy or discectomy. Presently,there is a need for interventional treatment for the large group ofpatients who ultimately do not undergo major spinal surgery, but whosustain significant disability due to various disorders or defects of anintervertebral disc. A common disorder of intervertebral discs is acontained herniation in which the nucleus pulposus does not breach theannulus fibrosus, but a protrusion of the disc causes compression of theexiting nerve root, leading to radicular pain. Typical symptoms are legpain compatible with sciatica. Such radicular pain may be considered asa particular form of discogenic pain. Most commonly, containedherniations leading to radicular pain are associated with the lumbarspine, and in particular with intervertebral discs at either L4-5 orL5-S1. Various disc defects are also encountered in the cervical spine.Methods and apparatus of the invention are applicable to all segments ofthe spine, including the cervical spine and the lumbar spine.

FIG. 53 schematically represents shaft 902 of probe 900 inserted withina nucleus pulposus of a disc having at least one fissure in the annulus.Shaft 902 may be conveniently inserted within the nucleus pulposus viaintroducer needle 928 in a minimally invasive percutaneous procedure. Ina preferred embodiment, a disc in the lumbar spine may be accessed via aposterior lateral approach, although other approaches are possible andare within the scope of the invention. The preferred length and diameterof shaft 902 and introducer needle 928 to be used in a procedure willdepend on a number of factors, including the region of the spine (e.g.,lumbar, cervical) or other body region to be treated, and the size ofthe patient. Preferred ranges for shaft 902 are given elsewhere herein.In one embodiment for treatment of a lumbar disc, introducer needle 928preferably has a diameter in the range of from about 50% to 150% theinternal diameter of a 17 Gauge needle. In an embodiment for treatmentof a cervical disc, introducer needle 928 preferably has a diameter inthe range of from about 50% to 150% the internal diameter of a 20 Gaugeneedle.

Shaft 902 includes an active electrode 910, as described hereinabove.Shaft 902 features curvature at distal end 902 a/902′a, for example, asdescribed with reference to FIGS. 47A–B. By rotating shaft 902 throughapproximately 180°, shaft distal end 902 a can be moved to a positionindicated by the dashed lines and labeled as 902′a. Thereafter, rotationof shaft 902 through an additional 180° defines a substantiallycylindrical three-dimensional space with a proximal frusto-conicalregion, the latter represented as a hatched area (shown between 902 aand 902′a). The bi-directional arrow distal to active electrode 910indicates translation of shaft 902 substantially along the longitudinalaxis of shaft 902. By a combination of axial and rotational movement ofshaft 902, a much larger volume of the nucleus pulposus can be contactedby electrode 910, as compared with a corresponding probe having a linear(non-curved) shaft. Furthermore, the curved nature of shaft 902 allowsthe surgeon to change the direction of advancement of shaft 902 byappropriate rotation thereof, and to guide shaft distal end 902 a to aparticular target site within the nucleus pulposus. In addition, furthercontrol may be exerted over which sites or regions within the disc canbe accessed by shaft distal end 902 a by advancing or retractingintroducer needle 928 to change the initiation point from which shaftdistal end 902 a may be guided or steered. Alternatively, selection ofan appropriate position from which shaft distal end 902 a may beadvanced, guided, or steered to a target location may make use of anintroducer extension tube (FIG. 61A) which acts as an extension ofintroducer needle 928. By changing the location of the introducer needleor the introducer extension tube relative to the disc, different regionsof the disc can be accessed by shaft distal end 902 a.

It is to be understood that according to certain embodiments of theinvention, the curvature of shaft 902 is the same, or substantially thesame, both prior to it being used in a surgical procedure and while itis performing ablation during a procedure, e.g., within anintervertebral disc. (One apparent exception to this statement, relatesto the stage in a procedure wherein shaft 902 may be transiently“molded” into a somewhat more linear configuration by the constraints ofintroducer inner wall 932 during housing, or passing, of shaft 902within introducer 928.) In contrast, certain prior art devices, andembodiments of the invention to be described hereinbelow (e.g., withreference to FIGS. 59A, 59B), may be linear or lacking a naturallydefined configuration prior to use, and then be steered into a selectedconfiguration during a surgical procedure.

While shaft distal end 902 a is at or adjacent to a target site withinthe nucleus pulposus, probe 900 may be used to ablate tissue byapplication of a first high frequency voltage between active electrode910 and return electrode 918 (e.g., FIG. 26B), wherein the volume of thenucleus pulposus is decreased, the pressure exerted by the nucleuspulposus on the annulus fibrosus is decreased, and at least one nerve ornerve root is decompressed. Accordingly, discogenic pain experienced bythe patient may be alleviated. Preferably, application of the first highfrequency voltage results in formation of a plasma in the vicinity ofactive electrode 910, and the plasma causes ablation by breaking downhigh molecular weight disc tissue components (e.g., proteins) into lowmolecular weight gaseous materials. Such low molecular weight gaseousmaterials may be at least partially vented or exhausted from the disc,e.g., by piston action, upon removal of shaft 902 and introducer 928from the disc and the clearance between introducer needle 928 and shaft902. In addition, by-products of tissue ablation may be removed by anaspiration device (not shown in FIG. 53), as is well known in the art.In this manner, the volume and/or mass of the nucleus pulposus may bedecreased.

In order to initiate and/or maintain a plasma in the vicinity of activeelectrode 910, a quantity of an electrically conductive fluid may beapplied to shaft 902 and/or the tissue to ablated. The electricallyconductive fluid may be applied to shaft 902 and/or to the tissue to beablated, either before or during application of the first high frequencyvoltage. Examples of electrically conductive fluids are saline (e.g.,isotonic saline), and an electrically conductive gel. An electricallyconductive fluid may be applied to the tissue to be ablated before orduring ablation. A fluid delivery unit or device may be a component ofthe electrosurgical probe itself, or may comprise a separate device,e.g., ancillary device 940 (FIG. 57). Alternatively, many body fluidsand/or tissues (e.g., the nucleus pulposus, blood) at the site to beablated are electrically conductive and can participate in initiation ormaintenance of a plasma in the vicinity of the active electrode.

In one embodiment, after ablation of nucleus pulposus tissue by theapplication of the first high frequency voltage and formation of acavity or channel within the nucleus pulposus, a second high frequencyvoltage may be applied between active electrode 910 and return electrode918, wherein application of the second high frequency voltage causescoagulation of nucleus pulposus tissue adjacent to the cavity orchannel. Such coagulation of nucleus pulposus tissue may lead toincreased stiffness, strength, and/or rigidity within certain regions ofthe nucleus pulposus, concomitant with an alleviation of discogenicpain. Furthermore, coagulation of tissues may lead to necrotic tissuewhich is subsequently broken down as part of a natural bodily processand expelled from the body, thereby resulting in de-bulking of the disc.Although FIG. 53 depicts a disc having fissures within the annulusfibrosus, it is to be understood that apparatus and methods of theinvention discussed with reference to FIG. 53 are also applicable totreating other types of disc disorders, including those described withreference to FIGS. 52B, 52D.

FIG. 54 shows shaft 902 of electrosurgical probe 900 within anintervertebral disc, wherein shaft distal end 902 a is targeted to aspecific site within the disc. In the situation depicted in FIG. 54, thetarget site is occupied by an errant fragment 291′ of nucleus pulposustissue. Shaft distal end 902 may be guided or directed, at least inpart, by appropriate placement of introducer 928, such that activeelectrode 910 is in the vicinity of fragment 291′. Preferably, activeelectrode 910 is adjacent to, or in contact with, fragment 291′.Although FIG. 54 depicts a disc in which a fragment of nucleus pulposusis targeted by shaft 902, the invention described with reference to FIG.54 may also be used for targeting other aberrant structures within anintervertebral disc, including annular fissures and containedherniations. In a currently preferred embodiment, shaft 902 includes atleast one curve (not shown in FIG. 54), and other features describedherein with reference to FIGS. 26A–35, wherein shaft distal end 902 amay be precisely guided by an appropriate combination of axial androtational movement of shaft 902. The procedure illustrated in FIG. 54may be performed generally according to the description presented withreference to FIG. 53. That is, shaft 902 is introduced into the disc viaintroducer 928 in a percutaneous procedure. After shaft distal end 902 ahas been guided to a target site, tissue at or adjacent to that site isablated by application of a first high frequency voltage. Thereafter,depending on the particular condition of the disc being treated, asecond high frequency voltage may optionally be applied in order tolocally coagulate tissue within the disc.

FIG. 55 schematically represents a series of steps involved in a methodof ablating disc tissue according to the present invention; wherein step1200 involves advancing an introducer needle towards an intervertebraldisc to be treated. The introducer needle has a lumen having a diametergreater than the diameter of the shaft distal end, thereby allowing freepassage of the shaft distal end through the lumen of the introducerneedle. In one embodiment, the introducer needle preferably has a lengthin the range of from about 3 cm to about 25 cm, and the lumen of theintroducer needle preferably has a diameter in the range of from about0.5 cm to about 2.5 mm. Preferably, the diameter of the shaft distal endis from about 30% to about 95% of the diameter of the lumen. Theintroducer needle may be inserted in the intervertebral discpercutaneously, e.g. via a posterior lateral approach. In oneembodiment, the introducer needle may have dimensions similar to thoseof an epidural needle, the latter well known in the art.

Optional step 1202 involves introducing an electrically conductivefluid, such as saline, into the disc. In one embodiment, in lieu of step1202, the ablation procedure may rely on the electrical conductivity ofthe nucleus pulposus itself. Step 1204 involves inserting the shaft ofthe electrosurgical probe into the disc, e.g., via the introducerneedle, wherein the distal end portion of the shaft bears an activeelectrode and a return electrode. In one embodiment, the shaft includesan outer shield, first and second curves at the distal end portion ofthe shaft, and an electrode head having an apical spike, generally asdescribed with reference to FIGS. 26A–32.

Step 1206 involves ablating at least a portion of disc tissue byapplication of a first high frequency voltage between the activeelectrode and the return electrode. In particular, ablation of nucleuspulposus tissue according to methods of the invention serves to decreasethe volume of the nucleus pulposus, thereby relieving pressure exertedon the annulus fibrosus, with concomitant decompression of a previouslycompressed nerve root, and alleviation of discogenic pain.

In one embodiment, the introducer needle is advanced towards theintervertebral disc until it penetrates the annulus fibrosus and entersthe nucleus pulposus. The shaft distal end in introduced into thenucleus pulposus, and a portion of the nucleus pulposus is ablated.These and other stages of the procedure may be performed underfluoroscopy to allow visualization of the relative location of theintroducer needle and shaft relative to the nucleus pulposus of thedisc. Additionally or alternatively, the surgeon may introduce theintroducer needle into the nucleus pulposus from a first side of thedisc, then advance the shaft distal end through the nucleus pulposusuntil resistance to axial translation of the electrosurgical probe isencountered by the surgeon. Such resistance may be interpreted by thesurgeon as the shaft distal end having contacted the annulus fibrosus atthe opposite side of the disc. Then, by use of depth markings on theshaft (FIG. 51A), the surgeon can retract the shaft a defined distancein order to position the shaft distal end at a desired location relativeto the nucleus pulposus. Once the shaft distal end is suitablypositioned, high frequency voltage may be applied to the probe via thepower supply unit.

After step 1206, optional step 1208 involves coagulating at least aportion of the disc tissue. In one embodiment, step 1206 results in theformation of a channel or cavity within the nucleus pulposus.Thereafter, tissue at the surface of the channel may be coagulatedduring step 1208. Coagulation of disc tissue may be performed byapplication of a second high frequency voltage, as describedhereinabove. After step 1206 or step 1208, the shaft may be moved (step1210) such that the shaft distal end contacts fresh tissue of thenucleus pulposus. The shaft may be axially translated (i.e. moved in thedirection of its longitudinal axis), may be rotated about itslongitudinal axis, or may be moved by a combination of axial androtational movement. In the latter case, a substantially spiral path isdefined by the shaft distal end. After step 1210, steps 1206 and 1208may be repeated with respect to the fresh tissue of the nucleus pulposuscontacted by the shaft distal end. Alternatively, after step 1206 orstep 1208, the shaft may be withdrawn from the disc (step 1212). Step1214 involves withdrawing the introducer needle from the disc. In oneembodiment, the shaft and the needle may be withdrawn from the discconcurrently. Withdrawal of the shaft from the disc may facilitateexhaustion of ablation by-products from the disc. Such ablationby-products include low molecular weight gaseous compounds derived frommolecular dissociation of disc tissue components, as describedhereinabove.

The above method may be used to treat any disc disorder in whichCoblation® and or coagulation of disc tissue is indicated, includingcontained herniations. In one embodiment, an introducer needle may beintroduced generally as described for step 1200, and a fluoroscopicfluid may be introduced through the lumen of the introducer needle forthe purpose of visualizing and diagnosing a disc defect or disorder.Thereafter, depending on the diagnosis, a treatment procedure may beperformed, e.g., according to steps 1202 through 1214, using the sameintroducer needle as access. In one embodiment, a distal portion, or theentire length, of the introducer needle may have an insulating coatingon its external surface. Such an insulating coating on the introducerneedle may prevent interference between the electrically conductiveintroducer needle and electrode(s) on the probe.

The size of the cavity or channel formed in a tissue by a singlestraight pass of the shaft through the tissue to be ablated is afunction of the diameter of the shaft (e.g., the diameter of the shaftdistal end and active electrode) and the amount of axial translation ofthe shaft. (By a “single straight pass” of the shaft is meant one axialtranslation of the shaft in a distal direction through the tissue, inthe absence of rotation of the shaft about the longitudinal axis of theshaft, with the power from the power supply turned on.) In the case of acurved shaft, according to various embodiments of the instant invention,a larger channel can be formed by rotating the shaft as it is advancedthrough the tissue. The size of a channel formed in a tissue by a singlerotational pass of the shaft through the tissue to be ablated is afunction of the deflection of the shaft, and the amount of rotation ofthe shaft about its longitudinal axis, as well as the diameter of theshaft (e.g., the diameter of the shaft distal end and active electrode)and the amount of axial translation of the shaft. (By a “singlerotational pass” of the shaft is meant one axial translation of theshaft in a distal direction through the tissue, in the presence ofrotation of the shaft about the longitudinal axis of the shaft, with thepower from the power supply turned on.) To a large extent, the diameterof a channel formed during a rotational pass of the shaft through tissuecan be controlled by the amount of rotation of the shaft, wherein the“amount of rotation” encompasses both the rate of rotation (e.g., theangular velocity of the shaft), and the number of degrees through whichthe shaft is rotated (e.g. the number of turns) per unit length of axialmovement. Typically, according to the invention, the amount of axialtranslation per pass (for either a straight pass or a rotational pass)is not limited by the length of the shaft. Instead, the amount of axialtranslation per single pass is preferably determined by the size of thetissue to be ablated. Depending on the size of the disc or other tissueto be treated, and the nature of the treatment, etc., a channel formedby a probe of the instant invention may preferably have a length in therange of from about 2 mm to about 50 mm, and a diameter in the range offrom about 0.5 mm to about 7.5 mm. In comparison, a channel formed by ashaft of the instant invention during a single rotational pass maypreferably have a diameter in the range of from about 1.5 mm to about 25mm.

A channel formed by a shaft of the instant invention during a singlestraight pass may preferably have a volume in the range of from about 1mm³, or less, to about 2,500 mm³. More preferably, a channel formed by astraight pass of a shaft of the instant invention has a volume in therange of from about 10 mm³ to about 2,500 mm³, and more preferably inthe range of from about 50 mm³ to about 2,500 mm³. In comparison, achannel formed by a shaft of the instant invention during a singlerotational pass typically has a volume from about twice to about 15times the volume of a channel of the same length formed during a singlerotational pass, i.e., in the range of from about 2 mm³ to about 4,000mm³, more preferably in the range of from about 50 mm³ to about 2,000mm³. While not being bound by theory, the reduction in volume of a dischaving one or more channels therein is a function of the total volume ofthe one or more channels.

FIG. 56 schematically represents a series of steps involved in a methodof guiding the distal end of a shaft of an electrosurgical probe to atarget site within an intervertebral disc for ablation of specificallytargeted disc tissue, wherein steps 1300 and 1302 are analogous to steps1200 and 1204 of FIG. 55. Thereafter step 1304 involves guiding theshaft distal end to a defined region within the disc. The specifictarget site may be pre-defined as a result of a previous procedure tovisualize the disc and its defect, e.g., via X-ray examination,endoscopically, or fluoroscopically. As an example, a defined targetsite within a disc may comprise a fragment of the nucleus pulposus thathas migrated within the annulus fibrosus (see, e.g., FIG. 52D) resultingin discogenic pain. However, guiding the shaft to defined sitesassociated with other types of disc disorders are also possible and iswithin the scope of the invention. In one embodiment, as a prelude toguiding the shaft distal end to a target site, the shaft distal end mayfirst be introduced into the disc at a selected location within thedisc. Such a selected location defines a space within the disc fromwhere the shaft distal end may be advanced in order to reach or accessthe target site. Preferably, the selected location defines a space inthe general vicinity of the target site from where the shaft distal endmay readily access the target site. The shaft distal end may beintroduced at the selected location within the disc by advancing orretracting the introducer needle within the disc until the introducerneedle distal end reaches the selected location. In another embodiment,the shaft distal end may be introduced at the selected location withinthe disc by advancing or retracting an introducer extension tube withinthe lumen of the introducer needle until the distal end of theintroducer extension tube reaches the selected location (FIGS. 62A–B).

Guiding the shaft distal end to the defined target site may be performedby axial and/or rotational movement of a curved shaft, as describedhereinabove. Or the shaft may be steerable, for example, by means of aguide wire, as is well known in the art. Guiding the shaft distal endmay be performed during visualization of the location of the shaftrelative to the disc, wherein the visualization may be performedendoscopically or via fluoroscopy. Endoscopic examination may employ afiber optic cable (not shown). The fiber optic cable may be integralwith the electrosurgical probe, or be part of a separate instrument(endoscope). Step 1306 involves ablating disc tissue, and is analogousto step 1206 (FIG. 55). Before or during step 1306, an electricallyconductive fluid may be applied to the disc tissue and/or the shaft inorder to provide a path for current flow between active and returnelectrodes on the shaft, and to facilitate and/or maintain a plasma inthe vicinity of the distal end portion of the shaft. After the shaftdistal end has been guided to a target site and tissue at that site hasbeen ablated, the shaft may be moved locally, e.g., within the sameregion of the nucleus pulposus, or to a second defined target sitewithin the same disc. The shaft distal end may be moved as describedherein (e.g., with reference to step 1210, FIG. 55). Or, according to analternative embodiment, the shaft may be steerable, e.g., by techniqueswell known in the art. Steps 1310 and 1312 are analogous to steps 1212and 1214, respectively (described with reference to FIG. 55).

It is known in the art that epidural steroid injections can transientlydiminish perineural inflammation of an affected nerve root, leading toalleviation of discogenic pain. In one embodiment of the invention,methods for ablation of disc tissue described hereinabove may beconveniently performed in conjunction with an epidural steroidinjection. For example, ablation of disc tissue and epidural injectioncould be carried out as part of a single procedure, by the same surgeon,using equipment common to both procedures (e.g. visualizationequipment). Combining Coblation® and epidural injection in a singleprocedure may provide substantial cost-savings to the healthcareindustry, as well as a significant improvement in patient care.

As alluded to hereinabove, methods and apparatus of the presentinvention can be used to accelerate the healing process ofintervertebral discs having fissures and/or contained herniations. Inone method, the present invention is useful in microendoscopicdiscectomy procedures, e.g., for decompressing a nerve root with alumbar discectomy. For example, as described above in relation to FIGS.18–20, a percutaneous penetration can be made in the patient's back sothat the superior lamina can be accessed. Typically, a small needle isused initially to localize the disc space level, and a guide wire isinserted and advanced under lateral fluoroscopy to the inferior edge ofthe lamina. Sequential cannulated dilators can be inserted over theguide wire and each other to provide a hole from the incision to thelamina. The first dilator may be used to “palpate” the lamina, assuringproper location of its tip between the spinous process and facet complexjust above the inferior edge of the lamina. A tubular retractor can thenbe passed over the largest dilator down to the lamina. The dilators canthen be removed, so as to establish an operating corridor within thetubular retractor. It should be appreciated however, that otherconventional or proprietary methods can be used to access the targetintervertebral disc. Once the target intervertebral disc has beenaccessed, an introducer device may be inserted into the intervertebraldisc.

With reference to FIG. 57, in one embodiment, both introducer needle 928and a second or ancillary introducer 938 may be inserted into the samedisc, to allow introduction of an ancillary device 940 into the targetdisc via ancillary introducer 938. Ancillary device 940 may comprise,for example, a fluid delivery device, a return electrode, an aspirationlumen, a second electrosurgical probe, or an endoscope having an opticalfiber component. Each of introducer needle 928 and ancillary introducer938 may be advanced through the annulus fibrosus until at least thedistal end portion of each introducer 928 and 938, is positioned withinthe nucleus pulposus. Thereafter, shaft 902″ of electrosurgical probe900′ may be inserted through at least one of introducers 928, 938, totreat the intervertebral disc. Typically, shaft 902″ of probe 900′ hasan outer diameter no larger than about 7 French (1 Fr: 0.33 mm), andpreferably between about 6 French and 7 French.

Prior to inserting electrosurgical probe 900 into the intervertebraldisc, an electrically conductive fluid can be delivered into the diskvia a fluid delivery assembly (e.g., ancillary device 940) in order tofacilitate or promote the Coblation® mechanism within the disc followingthe application of a high frequency voltage via probe 900′. By providinga separate device (940) for fluid delivery, the dimensions ofelectrosurgical probe 900′ can be kept to a minimum. Furthermore, whenthe fluid delivery assembly is positioned within ancillary introducer938, electrically conductive fluid can be conveniently replenished tothe interior of the disc at any given time during the procedure.Nevertheless, in other embodiments, the fluid delivery assembly can bephysically coupled to electrosurgical probe 900′.

In some methods, a radiopaque contrast solution (not shown) may bedelivered through a fluid delivery assembly so as to allow the surgeonto visualize the intervertebral disc under fluoroscopy. In someconfigurations, a tracking device 942 can be positioned on shaft distalend portion 902″a. Additionally or alternatively, shaft 902″ can bemarked incrementally, e.g., with depth markings 903, to indicate to thesurgeon how far the active electrode is advanced into the intervertebraldisc. In one embodiment, tracking device 942 includes a radiopaquematerial that can be visualized under fluoroscopy. Such a trackingdevice 942 and depth markings 903 provide the surgeon with means totrack the position of the active electrode 910 relative to a specifictarget site within the disc to which active electrode 910 is to beguided. Such specific target sites may include, for example, an annularfissure, a contained herniation, or a fragment of nucleus pulposus. Thesurgeon can determine the position of the active electrode 910 byobserving the depth markings 903, or by comparing tracking deviceoutput, and a fluoroscopic image of the intervertebral disc to apre-operative fluoroscopic image of the target intervertebral disc.

In other embodiments, an optical fiber (not shown) can be introducedinto the disc. The optical fiber may be either integral with probe 900′or may be introduced as part of an ancillary device 940 via ancillaryintroducer 938. In this manner, the surgeon can visually monitor theinterior of the intervertebral disc and the position of active electrode910.

In addition to monitoring the position of the distal portion ofelectrosurgical probe 900′, the surgeon can also monitor whether theprobe is in Coblation® mode. In most embodiments, power supply 28 (e.g.,FIG. 1) includes a controller having an indicator, such as a light, anaudible sound, or a liquid crystal display (LCD), to indicate whetherprobe 900′ is generating a plasma within the disc. If it is determinedthat the Coblation® mechanism is not occurring, (e.g., due to aninsufficiency of electrically conductive fluid within the disc), thesurgeon can then replenish the supply of the electrically conductivefluid to the disc.

FIG. 58 is a side view of an electrosurgical probe 900′ including shaft902′ having tracking device 942 located at distal end portion 902″a.Tracking device 942 may serve as a radiopaque marker adapted for guidingdistal end portion 902″a within a disc. Shaft 902″ also includes atleast one active electrode 910 disposed on the distal end portion 902″a.Preferably, electrically insulating support member or collar 916 ispositioned proximal of active electrode 910 to insulate active electrode910 from at least one return electrode 918. In most embodiments, thereturn electrode 918 is positioned on the distal end portion of theshaft 902″ and proximal of the active electrode 910. In otherembodiments, however, return electrode 918 can be omitted from shaft902″, in which case at least one return electrode may be provided onancillary device 940, or the return electrode may be positioned on thepatient's body, as a dispersive pad (not shown).

Although active electrode 910 is shown in FIG. 58 as comprising a singleapical electrode, other numbers, arrangements, and shapes for activeelectrode 910 are within the scope of the invention. For example, activeelectrode 910 can include a plurality of isolated electrodes in avariety of shapes. Active electrode 910 will usually have a smallerexposed surface area than return electrode 918, such that the currentdensity is much higher at active electrode 910 than at return electrode918. Preferably, return electrode 918 has a relatively large, smoothsurfaces extending around shaft 902″ in order to reduce currentdensities in the vicinity of return electrode 918, thereby minimizingdamage to non-target tissue.

While bipolar delivery of a high frequency energy is the preferredmethod of debulking the nucleus pulposus, it should be appreciated thatother energy sources (i.e., resistive, or the like) can be used, and theenergy can be delivered with other methods (i.e., monopolar, conductive,or the like) to debulk the nucleus.

FIG. 59A shows a steerable electrosurgical probe 950 including a shaft952, according to another embodiment of the invention. Preferably, shaft952 is flexible and may assume a substantially linear configuration asshown. Probe 950 includes handle 904, shaft distal end 952 a, activeelectrode 910, insulating collar 916, and return electrode 918. As canbe seen in FIG. 59B, under certain circumstances, e.g., upon applicationof a force to shaft 952 during guiding or steering probe 950 during aprocedure, shaft distal end 952 a can adopt a non-linear configuration,designated 952′a. The deformable nature of shaft distal end 952′a allowsactive electrode 910 to be guided to a specific target site within adisc.

FIG. 60 shows steerable electrosurgical probe 950 inserted within thenucleus pulposus of an intervertebral disc. An ancillary device 940 andancillary introducer 928 may also be inserted within the nucleuspulposus of the same disc. To facilitate the debulking of the nucleuspulposus adjacent to a contained herniation, shaft 952 (FIG. 59A) can bemanipulated to a non-linear configuration, represented as 952′.Preferably, shaft 952/952′ is flexible over at least shaft distal end952 a so as to allow steering of active electrode 910 to a positionadjacent to the targeted disc defect. The flexible shaft may be combinedwith a sliding outer shield, a sliding outer introducer needle, pullwires, shape memory actuators, and other known mechanisms (not shown)for effecting selective deflection of distal end 952 a to facilitatepositioning of active electrode 910 within a disc. Thus, it can be seenthat the embodiment of FIG. 60 may be used for the targeted treatment ofannular fissures, or any other disc defect for which Coblation® isindicated.

In one embodiment shaft 952 has a suitable diameter and length to allowthe surgeon to reach the target disc or vertebra by introducing theshaft through the thoracic cavity, the abdomen or the like. Thus, shaft952 may have a length in the range of from about 5.0 cm to 30.0 cm, anda diameter in the range of about 0.2 mm to about 20 mm. Alternatively,shaft 952 may be delivered percutaneously in a posterior lateralapproach. Regardless of the approach, shaft 952 may be introduced via arigid or flexible endoscope. In addition, it should be noted that themethods described with reference to FIGS. 57 and 60 may also beperformed in the absence of ancillary introducer 938 and ancillarydevice 940.

FIG. 61A shows an electrosurgical apparatus or system including a probe1050 in combination with an introducer extension tube 1054, according toanother aspect of the invention. Probe 1050 generally includes at leastone active electrode 910 disposed at a shaft distal end 1502 a, anelectrically insulating spacer or support 916 proximal to activeelectrode 910, and a return electrode 918 proximal to support 916. FIG.61A shows shaft distal end 1502 a positioned within introducer extensiontube 1054, which is in turn positioned within introducer needle 928.Introducer extension tube 1054 is adapted for passing shaft 1052therethrough, and for being passed within introducer needle 928.Introducer extension tube 1054 may be advanced distally from introducerdistal end 928 a to a site targeted for treatment, e.g., to a selectedlocation within an intervertebral disc. In this way, extension tubedistal end 1054 a (FIG. 61B) may define a starting point for advancementof shaft distal end 1052 a into the disc tissue, and in some embodimentsextension tube distal end 1054 a may define a starting point from whichguiding or steering of shaft distal end 1052 a is initiated. Byselecting a starting point within the disc from which guiding orsteering of shaft distal end 1052 a is initiated, much greater controlcan be exerted over accessing a given target site, and in addition amuch greater range of regions within the disc can be accessed with agiven probe (e.g., with a probe having a shaft of a given length andcurvature).

FIG. 61B shows shaft distal end 1052 a of the probe of FIG. 61Aextending beyond the distal end of both introducer extension tube 1054and introducer needle 928, with shaft distal end 1052 a adopting acurved configuration. Such a curved configuration allows access to amuch greater number of regions, or to a much larger volume of tissue,within an intervertebral disc, for example, by rotating shaft 1052. Sucha curved configuration may be due to a pre-defined bend or curve inshaft 1052 (e.g., FIGS. 47A–C), or may be the result of a steeringmechanism, the latter well known in the art. In the former situation, apre-defined curvature in shaft 1052 may be restrained or compressedwhile shaft 1052 is within introducer extension tube 1054 or introducerneedle 928. Introducer extension tube 1054 may be rigid or somewhatflexible. Introducer extension tube 1054 may be constructed from anelectrically conductive material such as stainless steel, and the like.Alternatively, introducer extension tube 1054 may be constructed from anelectrically insulating material, such as various plastics, and thelike.

FIG. 62A shows distal end 1054 a of introducer extension tube 1054advanced to a first position within an intervertebral disc 290. Shaft1052 lies within introducer extension tube 1054, which in turn lieswithin introducer needle 928. Needle distal end 928 a is introducedwithin disc 290, while extension tube distal end 1054 a is advancedslightly distal to needle distal end 928 a. Shaft distal end 1052 aextends beyond extension tube distal end 1054 a and adopts a curvedconfiguration to access a first region, R1, of nucleus pulposus 291.Curvature of shaft distal end 1052 a may result from a predefined biasor curve in shaft 1052, or shaft distal end 1052 a may be steerable.Certain other regions of disc 290 may be accessed by shaft distal end1052 a by circumferentially rotating shaft 1052 about its longitudinalaxis prior to shaft distal end 1052 a being advanced distally beyondextension tube distal end 1054 a (i.e., by rotating shaft 1052 whileshaft 1052 lies within introducer extension tube 1054).

FIG. 62B schematically represents a situation wherein extension tubedistal end 1054 a is advanced to a second position within intervertebraldisc 290. Much greater control can be exerted over the range of regionswithin disc 290 that can be accessed by shaft distal end 1052 a when thelocation of introducer extension tube 1054 is selected prior toadvancing shaft distal end 1052 a into the disc tissue. For example, asrepresented in FIG. 62B, by advancing introducer extension tube 1054distally within introducer needle 928 prior to advancing shaft distalend 1052 a from introducer extension tube 1054, shaft distal end 1052 acan readily access a second region R2, wherein R2 may be located remotefrom first region R1 (FIG. 62A). In contrast it is more problematic, ifnot impossible, for shaft distal end 1052 a to access region R2 whileintroducer extension tube 1054 is positioned in relation to the disc asshown in FIG. 62A. Similarly, without the use of introducer extensiontube 1054 (i.e., using an introducer needle 928 alone to advance shaft1052 into the disc) it is problematic, if not impossible, for shaftdistal end 1052 a to access region R2. The inclusion of an extensiondevice such as introducer extension tube 1054 as a component of theinstant invention provides major advantages in accessing a target sitewithin an intervertebral disc or other tissues.

Although certain embodiments of the invention have been describedprimarily with respect to treatment of intervertebral discs, it is to beunderstood that these methods and apparatus of the invention are alsoapplicable to the treatment of other tissues, organs, and bodilystructures. While the exemplary embodiments of the present inventionhave been described in detail, by way of example and for clarity ofunderstanding, a variety of changes, adaptations, and modifications willbe obvious to those of skill in the art. Therefore, the scope of thepresent invention is limited solely by the appended claims.

1. A method of treating an intervertebral disc having a nucleus pulposus and an annulus fibrosus, the method comprising: advancing a distal end of an electrosurgical instrument into the annulus fibrosus, wherein ar active electrode and a return electrode are positioned on the distal end of the electrosurgical instrument; moving the distal end of the electrosurgical instrument to a curved configuration that approximates a curvature of an inner surface of the annulus fibrosus; and delivering a high frequency voltage between the active electrode and the return electrode to treat the inner surface of the annulus fibrosus with a plasma in the vicinity of said active electrode, and wherein said active electrode having a shape and size different than said return electrode so as to create a higher current density at said active electrode than at said return electrode.
 2. The method of claim 1, wherein advancing comprises channeling through the annulus fibrosus by delivering a high frequency voltage between the active electrode and the return electrode.
 3. The method of claim 1 wherein moving comprises biasing the distal end.
 4. The method of claim 1 wherein moving comprises steering the distal end.
 5. The method of claim 4 wherein steering comprises actuating an actuator positioned at the proximal portion of the electrosurgical instrument.
 6. The method of claim 1 further comprising tracking the movement or location of the distal end of the electrosurgical instrument.
 7. The method of claim 6 wherein tracking comprises visualizing the distal end fluoroscopically.
 8. The method of claim 1 wherein advancing comprises positioning the active electrode and return electrode within the nucleus pulposus.
 9. The method of claim 1 wherein at least some tissue in contact with said plasma is ablated.
 10. The method of claim 9 wherein said tissue ablated comprises at least a portion of annulus fibrosis.
 11. The method of claim 9 wherein said tissue ablated comprises at least a portion of nucleus pulposus.
 12. The method of claim 1 further comprising providing an electrically conductive fluid from outside the body in the vicinity of said distal end to facilitate the format on of said plasma.
 13. A method of treating an intervertebral disc, the method comprising: positioning a distal end of an electrosurgical probe within close proximity of an outer surface of the intervertebral disc, the distal end of the electrosurgical probe comprising at least one active electrode; delivering a high frequency voltage between the at least one active electrode and a return electrode, the high frequency voltage being sufficient to create a channel in the disc tissue; advancing the active electrode through the channel created in the intervertebral disc; conforming the distal end of the electrosurgical probe to a curved configuration that approximates a curvature of an inner surface of an annulus fibrosus; and delivering a high frequency voltage between the active electrode and the return electrode to treat the inner surface of the annulus fibrosus.
 14. The method of claim 13 further comprising delivering a heating voltage between a coagulation electrode and the return electrode to heat at least a portion of the intervertebral disc, wherein the heating voltage is sufficient to coagulate a severed blood vessel, and the heating voltage is insufficient to induce molecular dissociation of disc tissue components ablate the intervertebral disc tissue.
 15. The method of claim 13 wherein conforming comprises biasing the distal end or steering the distal end.
 16. An apparatus for treating intervertebral discs, the apparatus comprising: a steerable shaft defining a shaft distal end portion, wherein the shaft distal end portion is moveable to a curved configuration that approximates the curvature of the inner surface of an annulus fibrosus; at least one active electrode positioned on the distal end portion of the shaft; a return electrode positioned proximal of the at least one active electrode; a high frequency energy source configured to create a voltage difference between the active electrode and the return electrode; and a coagulation electrode associated with the distal end portion and electrically coupled to said high frequency energy source.
 17. The apparatus of claim 16 further comprising a fluid delivery lumen configured to deliver a conductive fluid to the at least one active electrode.
 18. The apparatus of claim 17 further comprising an aspiration lumen adapted to aspirate the conductive fluid to a location adjacent the active electrode.
 19. The apparatus of claim 16, wherein the high frequency energy voltage source is configured to deliver a high frequency voltage to the coagulation electrode, wherein the high frequency voltage is insufficient for the coagulation electrode to produce an effect selected from the group consisting of: generating a plasma in the presence of an electrically conductive fluid, ablating tissue in a temperature range of 45° to 90° C., and causing molecular dissociation of tissue components. 